Lesson1 : Introduction to Visual Basic 6

1.1 The concept of computer programming

Before we begin Visual Basic 6 programming, let us understand some basic concepts of programming. According to Webopedia, a computer program is an organized list of instructions that, when executed, causes the computer to behave in a predetermined manner. Without programs, computers are useless. Therefore, programming means designing or creating a set of instructions to ask the computer to carry out certain jobs which normally are very much faster than human beings can do.

Many people think that computer is very intelligent, but in actual fact it is dumb and can't do anything without human assistance. The microchips of a CPU can only understand two distinct electrical states, namely, the on and off states, or 0 and 1 in the binary system. So, the CPU only understands a combinations of 0 and 1 code, a language which we called machine language. Machine language is extremely difficult to learn and it is not for us to master it easily.That's why modern programming languages supported by web hosting providers, such as PHP, Javascript, etc are all very high level. They allow us to communicate with the computer using language we can relate to, rather than machine language.

Fortunately , we have many smart programmers who can translate human language-like programs such as BASIC into machine language so that the computer can carry out the instructions entered by the users. Machine language is known as the primitive language while Interpreters and compilers like Visual Basic are called high-level language. Some of the high level computer languages beside Visual Basic are Fortran, Cobol, Java, C, C++, Turbo Pascal, flash action script, JavaScript, HTMLand more.

1.2 What is Visual Basic?

VISUAL BASIC is a high level programming language which evolved from the earlier DOS version called BASIC. BASIC means Beginners' All-purpose SymbolicInstruction Code. It is a relatively easy programming language to learn. The code looks a lot like English Language. Different software companies produced different versions of BASIC, such as Microsoft QBASIC, QUICKBASIC, GWBASIC ,IBM BASICA and so on. However, people prefer to use Microsoft Visual Basic today, as it is a well developed programming language and supporting resources are available everywhere. Now, there are many versions of VB exist in the market, the most popular one and still widely used by many VB programmers is none other than Visual Basic 6 . We also have VB.net, Visual Basic 2005, Visual Basic 2008 and the latest Visual Basic 2010 . Both Vb2008 and VB2010 are fully object oriented programming (OOP) languages.

VISUAL BASIC is a VISUAL and Event-driven Programming Language. These are the main divergence from the old BASIC. In BASIC, programming is done in a text-only environment and the program is executed sequentially. In VB6, programming is done in a graphical environment. In the old BASIC, you have to write program code for each graphical object you wish to display it on screen, including its position and its color. However, In VB6 , you just need to drag and drop any graphical object anywhere on the form, and you can change its properties using the properties window.

In addition, Visual Basic 6 is Event-driven because we need to write code in order to perform some tasks in response to certain events. The events usually comprises but not limited to the user's inputs. Some of the events are load, click, double click, drag and drop, pressing the keys and more. We will learn more about events in later lessons. Therefore, a VB6 Program is made up of many subprograms, each has its own program code, and each can be executed independently and at the same time each can be linked together in one way or another.

1.3 What programs can you create with Visual Basic 6?

With VB 6, you can create any program depending on your objective. For example, if you are a college or university lecturer, you can create educational programs to teach business, mathematics, science, economics, engineering, computer science, accountancy , financial management, information system and more to make teaching more effective and interesting. For example, you can create mathematical programs such as Geometric Progression, Quadratic Equation Solver, Simultaneous Equation Solver ,Prime Number, Factors Finder, Quadratic Function Graph Plotter and so on. For science teacher, you can create simulation programs such as Projectile, Simple Harmonic Motion, Star War etc. If you are in business, you can also create business programs such asinventory management system , Amortization Calculator , investments calculator, point-of-sale system, payroll system, accounting program and more to help manage your business and increase productivity. For those of you who like games , you can create those programs such as slot machine, reversi, tic tac toeand more. Besides, you can create multimedia programs such as Smart Audio Player, Multimedia Player and so on. Indeed, there is no limit to what program you can create ! There are many such programs in this tutorial, so you must spend more time on the tutorial in order to learn how to create those programs.

1.4 The Visual Basic 6 Integrated Development Environment

Before you can program in VB 6, you need to install Visual Basic 6 compiler in your computer. You can purchase a copy of Microsoft Visual Basic 6.0 Learning Edition or Microsoft Visual Basic Professional 6.0 with Plus Pack from Amazon.com, both are vb6 compilers. If you have already installed Microsoft Office in your PC or laptop, you can also use the built-in Visual Basic Application in Excel to start creating Visual Basic programs without having to spend extra cash to buy the VB6 compiler.

After installing vb6 compiler, the icon with appear on your desktop or in your programs menu. Click on the icon to launch the VB6 compiler. On start up, Visual Basic 6.0 will display the following dialog box as shown in Figure 1.1.

Figure 1.1: New Project Dialog

You can choose to either start a new project, open an existing project or select a list of recently opened programs. A project is a collection of files that make up your application. There are various types of applications that we could create, however, we shall concentrate on creating Standard EXE programs (EXE means executable). Before you begin, you must think of an application that might be useful, have commercial values . educational or recreational. click on the Standard EXE icon to go into the actual Visual Basic 6 programming environment.

When you start a new Visual Basic 6 Standard EXE project, you will be presented with the Visual Basic 6 Integrated Development Environment (IDE). The Visual Basic 6 Integrated Programming Environment is show in Figure 1.2. It consists of the toolbox, the form, the project explorer and the properties window.

Figure 1.2: VB6 Programming Environment

Form is the primary building block of a Visual Basic 6 application. A Visual Basic 6 application can actually comprises many forms; but we shall focus on developing an application with one form first. We will learn how to develop applications with multiple forms later. Before you proceed to build the application, it is a good practice to save the project first. You can save the project by selecting Save Project from the File menu, assign a name to your project and save it in a certain folder.

Lesson 2: Building Visual Basic Applications

2.1 Creating Your First Application

In this lesson, we will not delve into the technical aspects of Visual Basic programming yet, what you need to do is to try out the examples below to see how does a Visual Basic program looks like:

Example 2.1.1 is a simple program. First of all, you have to launch Microsoft Visual Basic 6. Normally, a default form with the name Form1 will be available for you to start your new project. Now, double click on Form1, the source code window for Form1 as shown in figure 2.1 will appear. The top of the source code window consists of a list of objects and their associated events or procedures. In figure 2.1, the object displayed is Form and the associated procedure is Load.

Figure 2.1 Source Code Window

When you click on the object box, the drop-down list will display a list of objects you have inserted into your form as shown in figure 2.2. Here, you can see a form with the name Form1, a command button with the name Command1, a Label with the name Label1 and a Picture Box with the name Picture1. Similarly, when you click on the procedure box, a list of procedures associated with the object will be displayed as shown in figure 2.3. Some of the procedures associated with the object Form1 are Activate, Click, DblClick (which means Double-Click) , DragDrop, keyPress and more. Each object has its own set of procedures. You can always select an object and write codes for any of its procedure in order to perform certain tasks.

You do not have to worry about the beginning and the end statements (i.e. Private Sub Form_Load.......End Sub.); Just key in the lines in between the above two statements exactly as are shown here. When you press F5 to run the program, you will be surprised that nothing shown up .In order to display the output of the program, you have to add the Form1.show statement like in Example 2.1.1 or you can just use Form_Activate ( ) event procedure as shown in example 2.1.2. The command Print does not mean printing using a printer but it means displaying the output on the computer screen. Now, press F5 or click on the run button to run the program and you will get the output as shown in figure 2.4.

You can also perform arithmetic calculations as shown in example 2.1.2. VB uses * to denote the multiplication operator and / to denote the division operator. The output is shown in figure 2.3, where the results are arranged vertically.

Figure 2.2: List of Objects

Figure 2.3: List of Procedures

Example 2.1.1 Private Sub Form_Load ( ) Form1.show Print “Welcome to Visual Basic tutorial” End Sub	Figure 2.4 : The output of example 2.1.1
Example 2.1.2 Private Sub Form_Activate ( ) Print 20 + 10 Print 20 - 10 Print 20 * 10 Print 20 / 10 End Sub	Figure 2.5: The output of example 2.1.2

You can also use the + or the & operator to join two or more texts (string) together like in example 2.1.4 (a) and (b)

Example 2.1.4(a)

Private Sub

A = "Tom"
B = “likes"
C = “to"
D = “eat"
E = “burger"
Print A + B + C + D + E

End Sub

Example 2.1.4(b)

Private Sub

A = "Tom"
B = “likes"
C = “to"
D = “eat"
E = “burger"
Print A & B & C & D & E

End Sub

The Output of Example 2.1.4(a) &(b) is as shown in Figure 2.7.

Figure 2.7

2.2 Steps in Building a Visual Basic Application

Step 1 : Design the interface by adding controls to the form and set their properties

Step 2 : Write code for the event procedures

Lesson 3-Working With Controls

3.1 The Control Properties

Before writing an event procedure for the control to response to an event, you have to set certain properties for the control to determine its appearance and how will it work with the event procedure. You can set the properties of the controls in the properties window or at runtime.

Figure 3.1 on the right is a typical properties window for a form. You can rename the form caption to any name that you like best. In the properties window, the item appears at the top part is the object currently selected (in Figure 3.1, the object selected is Form1). At the bottom part, the items listed in the left column represent the names of various properties associated with the selected object while the items listed in the right column represent the states of the properties. Properties can be set by highlighting the items in the right column then change them by typing or selecting the options available.

For example, in order to change the caption, just highlight Form1 under the name Caption and change it to other names. You may also try to alter the appearance of the form by setting it to 3D or flat. Other things you can do are to change its foreground and background color, change the font type and font size, enable or disable minimize and maximize buttons and etc.

You can also change the properties at runtime to give special effects such as change of color, shape, animation effect and so on. For example the following code will change the form color to red every time the form is loaded. VB uses hexadecimal system to represent the color. You can check the color codes in the properties windows which are showed up under ForeColor and BackColor .

Private Sub Form_Load()

Form1.Show
Form1.BackColor = &H000000FF&

End Sub

Another example is to change the control Shape to a particular shape at runtime by writing the following code. This code will change the shape to a circle at runtime.

Private Sub Form_Load()

Shape1.Shape = 3

End Sub

Figure 3.1

I would like to stress that knowing how and when to set the objects' properties is very important as it can help you to write a good program or you may fail to write a good program. So, I advice you to spend a lot of time playing with the objects' properties.

We are not going into the details on how to set the properties. However, I would like to stress a few important points about setting up the properties.

You should set the Caption Property of a control clearly so that a user knows what to do with that command.
Use a meaningful name for the Name Property because it is easier to write and read the event procedure and easier to debug or modify the programs later.
One more important property is whether to make the control enabled or not.
Finally, you must also considering making the control visible or invisible at runtime, or when should it become visible or invisible.

3.2 Handling some of the common controls

Figure 3.2 below is the VB6 toolbox that shows the basic controls.

Figure 3.2: Toolbox

3.2.1 The Text Box

The text box is the standard control for accepting input from the user as well as to display the output. It can handle string (text) and numeric data but not images or pictures. Just like text fields in websites, powered not by Windows, but typically linux web hosting platforms like iPage, these fields collect user input.String in a text box can be converted to a numeric data by using the function Val(text). The following example illustrates a simple program that processes the input from the user.

Example 3.1

In this program, two text boxes are inserted into the form together with a few labels. The two text boxes are used to accept inputs from the user and one of the labels will be used to display the sum of two numbers that are entered into the two text boxes. Besides, a command button is also programmed to calculate the sum of the two numbers using the plus operator. The program use creates a variable sum to accept the summation of values from text box 1 and text box 2.The procedure to calculate and to display the output on the label is shown below. The output is shown in Figure 3.3

Private Sub Command1_Click()

‘To add the values in text box 1 and text box 2

Sum = Val(Text1.Text) + Val(Text2.Text)

‘To display the answer on label 1

Label1.Caption = Sum

End Sub

Figure 3.3

3.2.2 The Label

The label is a very useful control for Visual Basic, as it is not only used to provide instructions and guides to the users, it can also be used to display outputs. One of its most important properties is Caption. Using the syntax label.Caption, it can display text and numeric data . You can change its caption in the properties window and also at runtime. Please refer to Example 3.1 and Figure 3.1 for the usage of label.

3.2.3 The Command Button

The command button is one of the most important controls as it is used to execute commands. It displays an illusion that the button is pressed when the user click on it. The most common event associated with the command button is the Click event, and the syntax for the procedure is

Private Sub Command1_Click ()

Statements

End Sub

3.2.4 The Picture Box

The Picture Box is one of the controls that is used to handle graphics. You can load a picture at design phase by clicking on the picture item in the properties window and select the picture from the selected folder. You can also load the picture at runtime using the LoadPicture method. For example, the statement will load the picture grape.gif into the picture box.

Picture1.Picture=LoadPicture ("C:\VB program\Images\grape.gif")

You will learn more about the picture box in future lessons. The image in the picture box is not resizable.

3.2.5 The Image Box

The Image Box is another control that handles images and pictures. It functions almost identically to the picture box. However, there is one major difference, the image in an Image Box is stretchable, which means it can be resized. This feature is not available in the Picture Box. Similar to the Picture Box, it can also use the LoadPicture method to load the picture. For example, the statement loads the picture grape.gif into the image box.

Image1.Picture=LoadPicture ("C:\VB program\Images\grape.gif")

3.2.6 The List Box

The function of the List Box is to present a list of items where the user can click and select the items from the list. In order to add items to the list, we can use the AddItem method. For example, if you wish to add a number of items to list box 1, you can key in the following statements

Example 3.2

Private Sub Form_Load ( )

List1.AddItem “Lesson1”

List1.AddItem “Lesson2”

List1.AddItem “Lesson3”

List1.AddItem “Lesson4”

End Sub

The items in the list box can be identified by the ListIndex property, the value of the ListIndex for the first item is 0, the second item has a ListIndex 1, and the third item has a ListIndex 2 and so on

3.2.7 The Combo Box

The function of the Combo Box is also to present a list of items where the user can click and select the items from the list. However, the user needs to click on the small arrowhead on the right of the combo box to see the items which are presented in a drop-down list. In order to add items to the list, you can also use the AddItem method. For example, if you wish to add a number of items to Combo box 1, you can key in the following statements

Example 3.3

Private Sub Form_Load ( )

Combo1.AddItem “Item1”

Combo1.AddItem “Item2”

Combo1.AddItem “Item3”

Combo1.AddItem “Item4”

End Sub

3.2.8 The Check Box

The Check Box control lets the user selects or unselects an option. When the Check Box is checked, its value is set to 1 and when it is unchecked, the value is set to 0. You can include the statements Check1.Value=1 to mark the Check Box and Check1.Value=0 to unmark the Check Box, as well as use them to initiate certain actions. For example, the program will change the background color of the form to red when the check box is unchecked and it will change to blue when the check box is checked. You will learn about the conditional statement If….Then….Elesif in later lesson. VbRed and vbBlue are color constants and BackColor is the background color property of the form.

Example 3.4

Private Sub Command1_Click()

If Check1.Value = 1 And Check2.Value = 0 Then
MsgBox "Apple is selected"
ElseIf Check2.Value = 1 And Check1.Value = 0 Then
MsgBox "Orange is selected"
Else
MsgBox "All are selected"
End If

End Sub

3.2.9 The Option Box

The Option Box control also lets the user selects one of the choices. However, two or more Option Boxes must work together because as one of the Option Boxes is selected, the other Option Boxes will be unselected. In fact, only one Option Box can be selected at one time. When an option box is selected, its value is set to “True” and when it is unselected; its value is set to “False”. In the following example, the shape control is placed in the form together with six Option Boxes. When the user clicks on different option boxes, different shapes will appear. The values of the shape control are 0, 1, and 2,3,4,5 which will make it appear as a rectangle, a square, an oval shape, a rounded rectangle and a rounded square respectively.

Example 3.5

Private Sub Option1_Click ( )

Shape1.Shape = 0

End Sub

Private Sub Option2_Click()

Shape1.Shape = 1

End Sub

Private Sub Option3_Click()

Shape1.Shape = 2

End Sub

Private Sub Option4_Click()

Shape1.Shape = 3

End Sub

Private Sub Option5_Click()

Shape1.Shape = 4

End Sub

Private Sub Option6_Click()

Shape1.Shape = 5

End Sub

3.2.10 The Drive List Box

The Drive ListBox is for displaying a list of drives available in your computer. When you place this control into the form and run the program, you will be able to select different drives from your computer as shown in Figure 3.4

Figure 3.4 The Drive List Box

3.2.11 The Directory List Box

The Directory List Box is for displaying the list of directories or folders in a selected drive. When you place this control into the form and run the program, you will be able to select different directories from a selected drive in your computer as shown in Figure 3.5

Figure 3.5 The Directory List Box

3.2.12 The File List Box

The File List Box is for displaying the list of files in a selected directory or folder. When you place this control into the form and run the program, you will be able to shown the list of files in a selected directory as shown in Figure 3.6

Figure 3.6 The File List Box

You can coordinate the Drive List Box, the Directory List Box and the File List Box to search for the files you want. The procedure will be discussed in later lessons.

Lesson 4 : Writing the Code

In lesson 2, you have learned how to enter the program code and run the sample VB programs but without much understanding about the logics of VB programming. Now, let’s get down to learning some basic rules about writing the VB program code.

Each control or object in VB can usually run many kinds of events or procedures; these events are listed in the dropdown list in the code window that is displayed when you double-click on an object and click on the procedures’ box(refer to Figure 2.3). Among the events are loading a form, clicking of a command button, pressing a key on the keyboard or dragging an object and more. For each event, you need to write an event procedure so that it can perform an action or a series of actions

To start writing an event procedure, you need to double-click an object. For example, if you want to write an event procedure when a user clicks a command button, you double-click on the command button and an event procedure will appear as shown in Figure 2.1. It takes the following format:

Private Sub Command1_Click

(Key in your program code here)

End Sub

You then need to key-in the procedure in the space between Private Sub Command1_Click............. End Sub. Sub actually stands for sub procedure that made up a part of all the procedures in a program. The program code is made up of a number of statements that set certain properties or trigger some actions. The syntax of Visual Basic’s program code is almost like the normal English language though not exactly the same, so it is very easy to learn.

The syntax to set the property of an object or to pass certain value to it is :

Object.Property
where Object and Property is separated by a period (or dot). For example, the statement Form1.Show means to show the form with the name Form1, Iabel1.Visible=true means label1 is set to be visible,Text1.text=”VB” is to assign the text VB to the text box with the name Text1, Text2.text=100 is to pass a value of 100 to the text box with the name text2, Timer1.Enabled=False is to disable the timer with the name Timer1 and so on. Let’s examine a few examples below:

Example 4.1
Private Sub Command1_click

Label1.Visible=false

Label2.Visible=True

Text1.Text=”You are correct!”

End sub

Example 4.2

Private Sub Command1_click

Label1.Caption=” Welcome”

Image1.visible=true

End sub

Example 4.3

Private Sub Command1_click

Pictuire1.Show=true

Timer1.Enabled=True

Lable1.Caption=”Start Counting

End sub

In Example 4.1, clicking on the command button will make label1 become invisible and label2 become visible; and the text” You are correct” will appear in TextBox1. In example 4.2, clicking on the command button will make the caption label1 change to “Welcome” and Image1 will become visible. In example 4.3 , clicking on the command button will make Picture1 show up, timer starts running and the caption of label1 change to “Start Counting”. This type of operation could be particularly useful in applications such as a website stat counter (most web hosting plans include some analytics or stat package).

Syntaxes that do not involve setting of properties are also English-like, some of the commands are Print, If…Then….Else….End If, For…Next, Select Case…..End Select , End and Exit Sub. For example, Print “ Visual Basic” is to display the text Visual Basic on screen and End is to end the program. Other commands will be explained in details in the coming lessons.

Program code that involve calculations is very easy to write, you need to write them almost like you do in mathematics. However, in order to write an event procedure that involves calculations, you need to know the basic arithmetic operators in VB as they are not exactly the same as the normal operators we use, except for + and - . For multiplication, we use *, for division we use /, for raising a number x to the power of n, we use x ^n and for square root, we use Sqr(x). VB offers many more advanced mathematical functions such as Sin, Cos, Tan and Log, they will be discussed in lesson 10. There are also two important functions that are related to arithmetic operations, i.e. the functions Val and Str$ where Val is to convert text entered into a textbox to numerical value and Str$ is to display a numerical value in a textbox as a string (text). While the function Str$ is as important as VB can display a numeric values as string implicitly, failure to use Val will results in wrong calculation. Let’s examine example 4.4 and example 4.5.

Example 4.4

Private Sub Form_Activate()

Text3.text=text1.text+text2.text

End Sub

Example 4.5

Private Sub Form_Activate()

Text3.text=val(text1.text)+val(text2.text)

End Sub

When you run the program in example 4.4 and enter 12 in textbox1 and 3 in textbox2 will give you a result of 123, which is wrong. It is because VB treat the numbers as string and so it just joins up the two strings. On the other hand, running exampled 4.5 will give you the correct result, i.e., 15.

Lesson 5: Managing Visual Basic Data

There are many types of data that we come across in our daily life. For example, we need to handle data such as names, addresses, money, date, stock quotes, statistics and more everyday. Similarly in Visual Basic, we have to deal with all sorts of of data, some can be mathematically calculated while some are in the form of text or other forms. VB divides data into different types so that it is easier to manage when we need to write the code involving those data.

5.1 Visual Basic Data Types

Visual Basic classifies the information mentioned above into two major data types, they are the numeric data types and the non-numeric data types.

5.1.1 Numeric Data Types

Numeric data types are types of data that consist of numbers, which can be computed mathematically with various standard operators such as add, minus, multiply, divide and more. Examples of numeric data types are examination marks, height, weight, the number of students in a class, share values, price of goods, monthly bills, fees and others.

In Visual Basic, numeric data are divided into 7 types, depending on the range of values they can store. Calculations that only involve round figures or data that does not need precision can use Integer or Long integer in the computation. Programs that require high precision calculation need to use Single and Double decision data types, they are also called floating point numbers. For currency calculation , you can use the currency data types. Lastly, if even more precision is required to perform calculations that involve a many decimal points, we can use the decimal data types. These data types summarized in Table 5.1

Table 5.1: Numeric Data Types

Type	Storage	Range of Values
Byte	1 byte	0 to 255
Integer	2 bytes	-32,768 to 32,767
Long	4 bytes	-2,147,483,648 to 2,147,483,648
Single	4 bytes	-3.402823E+38 to -1.401298E-45 for negative values 1.401298E-45 to 3.402823E+38 for positive values.
Double	8 bytes	-1.79769313486232e+308 to -4.94065645841247E-324 for negative values 4.94065645841247E-324 to 1.79769313486232e+308 for positive values.
Currency	8 bytes	-922,337,203,685,477.5808 to 922,337,203,685,477.5807
Decimal	12 bytes	+/- 79,228,162,514,264,337,593,543,950,335 if no decimal is use +/- 7.9228162514264337593543950335 (28 decimal places).

5.1.2 Non-numeric Data Types

Nonnumeric data types are data that cannot be manipulated mathematically using standard arithmetic operators. The non-numeric data comprises text or string data types, the Date data types, the Boolean data types that store only two values (true or false), Object data type and Variant data type .They are summarized in Table 5.2

Table 5.2: Nonnumeric Data Types

Data Type	Storage	Range
String(fixed length)	Length of string	1 to 65,400 characters
String(variable length)	Length + 10 bytes	0 to 2 billion characters
Date	8 bytes	January 1, 100 to December 31, 9999
Boolean	2 bytes	True or False
Object	4 bytes	Any embedded object
Variant(numeric)	16 bytes	Any value as large as Double
Variant(text)	Length+22 bytes	Same as variable-length string

5.1.3 Suffixes for Literals

Literals are values that you assign to data. In some cases, we need to add a suffix behind a literal so that VB can handle the calculation more accurately. For example, we can use num=1.3089# for a Double type data. Some of the suffixes are displayed in Table 5.3.

Table 5.3

Suffix	Data Type
&	Long
!	Single
#	Double
@	Currency

In addition, we need to enclose string literals within two quotations and date and time literals within two # sign. Strings can contain any characters, including numbers. The following are few examples:
memberName="Turban, John."
TelNumber="1800-900-888-777"
LastDay=#31-Dec-00#
ExpTime=#12:00 am#

5.2 Managing Variables

Variables are like mail boxes in the post office. The contents of the variables changes every now and then, just like the mail boxes. In term of VB, variables are areas allocated by the computer memory to hold data. Like the mail boxes, each variable must be given a name. To name a variable in Visual Basic, you have to follow a set of rules. All modern programming languages such as PHP (PHP runs on hosts like iPage - see review) allow us developers to use variables to store and retrieve data. Each language has its own special syntax to learn.

5.2.1 Variable Names

The following are the rules when naming the variables in Visual Basic

It must be less than 255 characters
No spacing is allowed
It must not begin with a number
Period is not permitted

Examples of valid and invalid variable names are displayed in Table 5.4

Table 5.4

Valid Name	Invalid Name
My_Car	My.Car
ThisYear	1NewBoy
Long_Name_Can_beUSE	He&HisFather *& is not acceptable

5.2.2 Declaring Variables Explicitly

In Visual Basic, it is a good practice to declare the variables before using them by assigning names and data types. They are normally declared in the general section of the codes' windows using the Dim statement. You can use any variable to hold any data , but different types of variables are designed to work efficiently with different data types .
The form is as follows:

Dim VariableName As DataType

If you want to declare more variables, you can declare them in separate lines or you may also combine more in one line , separating each variable with a comma, as follows:

Dim VariableName1 As DataType1, VariableName2 As DataType2, VariableName3 As DataType3

Example 5.1

Dim password As String

Dim yourName As String

Dim firstnum As Integer

Dim secondnum As Integer

Dim total As Integer

Dim doDate As Date

Dim password As String,  yourName As String, firstnum As Integer

Unlike other programming languages, Visual Basic actually doesn't require you to specifically declare a variable before it's used. If a variable isn't declared, VB will automatically declare the variable as a Variant. A variant is data type that can hold any type of data.

For string declaration, there are two possible types, one for the variable-length string and another for the fixed-length string. For the variable-length string, just use the same format as example 5.1 above. However, for the fixed-length string, you have to use the format as shown below:

Dim VariableName as String * n, where n defines the number of characters the string can hold.

Example 5.2:

Dim yourName as String * 10

yourName can holds no more than 10 Characters.

5.2.2 Scope of Declaration

Other than using the Dim keyword to declare the data, you can also use other keywords to declare the data. Three other keywords are private ,static and public. The forms are as shown below:

Private VariableName as Datatype

Static VariableName as Datatype

Public VariableName as Datatype

The above keywords indicate the scope of declaration. Private declares a local variable, or a variable that is local to a procedure or module. However, Private is rarely used, we normally use Dim to declare a local variable. The Static keyword declares a variable that is being used multiple times, even after a procedure has been terminated. Most variables created inside a procedure are discarded by Visual Basic when the procedure is finished, static keyword preserve the value of a variable even after the procedure is terminated. Public is the keyword that declares a global variable, which means it can be used by all the procedures and modules of the whole program.

5.3 Constants

Constants are different from variables in the sense that their values do not change during the running of the program.

5.3.1 Declaring a Constant

The format to declare a constant is
Const Constant Name As Data Type = Value
Example 5.3
Const Pi As Single=3.142
Const Temp As Single=37
Const Score As Single=100

Lesson 6: Working with Variables

6.1 Assigning Values to Variables

After declaring various variables using the Dim keywords or other keywords, we need to assign values or information to those variables. Assigning a value to a variable means storing the value in that variable. The form of an assignment statement is as follows:

Variable=Expression

The variable can be a declared variable or a control's property value. The expression could be a mathematical expression, a number, a literal value, a string, a Boolean value (true or false) , a combination of other variables and constants, a function and more. The following are some examples:

FirstNumber=100
SecondNumber=FirstNumber-99
userName="John Lyan"
userpass.Text = password
Label1.Visible = True
Command1.Visible = false
Label4.Caption = textbox1.Text
ThirdNumber = Val(usernum1.Text)
Total = firstNumber + secondNumber +ThirdNumber
MeanScore% = SumScores% / NumSubjects%
X=sqr (16)
TrimString= Ltrim (“ Visual Basic”, 4)
Num=Int(Rnd*6)+1

A type mismatch error occurs when you try to assign a value to a variable of incompatible data type. For example, if you have declared a variable as an integer but you assigned a string value to it, a type mismatch error occurred, as shown in Example 6.1:

Example 6.1

Private Sub Command1_Click()
Dim MyNumber As Integer
MyNumber = "Happy Birthday!"
Text1.Text = MyNumber
End Sub

When you run the program, type mismatch occurred, as shown in Figure 6.1

6.2 Using Operators in Visual Basic

To compute inputs from users and to generate results, we need to use various mathematical operators. In Visual Basic, except for + and -, the symbols for the operators are different from normal mathematical operators, as shown in Table 6.1.

Table 6.1: Arithmetic Operators

Operator	Mathematical function	Example
^	Exponential	2^4=16
*	Multiplication	4*3=12,
/	Division	12/4=3
Mod	Modulus (returns the remainder from an integer division)	15 Mod 4=3
\	Integer Division(discards the decimal places)	19\4=4
+ or &	String concatenation	"Visual"&"Basic"="Visual Basic"

Example 6.2

In this example, three variables are declared as string. For variables FirstName and SecondName will receive their data from the user’s input into textbox1 and textbox2, and the variable YourName will be assigned the data by combining the first two variables. Finally, YourName is displayed on Label1. The output is shown in Figure 6.2:

Private Sub Command1_Click()

Dim FirstName As String

Dim LastName As String

Dim YourName As String

FirstName = Text1.Text

LastName = Text2.Text

YourName = FirstName + " " + LastName

Label1.Caption = YourName

End Sub

Figure 6.2

Example 6.3

In this example, three variables are declared as integer and two variables are declared as variant. Variant means the variable can hold any data type. The program computes the total and average of the three numbers that are entered into three text boxes.

Private sub Form_Click

Dim number1, number2, number3 as Integer

Dim total, average as variant

number1=val(Text1.Text)
number2=val(Text2.Text)
number3= val(Text3.Text)

Total=number1+number2+number3

Average=Total/5

Label1.Caption=Total

Label2.Caption=Average

End Sub

Lesson 7 : Controlling Program Flow

In previous lessons, we have learned how to create Visual Basic 6 code that can accept input from the user and display the output without controlling the program flow. In this lesson, you will learn how to create Visual Basic 6 code that can make decision when it process input from the user, and control the program flow in the process. Decision making process is an important part of programming because it can help to solve practical problems intelligently so that it can provide useful output or feedback to the user. For example, we can write a program that can ask the computer to perform certain task until a certain condition is met.

7.1 Conditional Operators

To control the VB program flow, we can use various conditional operators. Basically, they resemble mathematical operators. Conditional operators are very powerful tools, they let the Visual Basic 6 program compare data values and then decide what action to take, whether to execute a program or terminate the program and more. These operators are shown in Table 7.1.
Table 7.1: Conditional Operators

Operator	Meaning
=	Equal to
>	More than
<	Less Than
>=	More than or equal
<=	Less than or equal
<>	Not Equal to

7.2 Logical Operators

In addition to conditional operators, there are a few logical operators which offer added power to the VB programs. There are shown in Table 7.2.

Table 7.2:Logical Operators

Operator	Meaning
And	Both sides must be true
or	One side or other must be true
Xor	One side or other must be true but not both
Not	Negates truth

* You can also compare strings with the above operators. However, there are certain rules to follows: Upper case letters are less than lowercase letters, "A"<"B"<"C"<"D".......<"Z" and number are less than letters.

7.3 Using If.....Then.....Else Statements with Operators

To effectively control the VB program flow, we shall use If...Then...Else statement together with the conditional operators and logical operators.
The general format for the if...then...else statement is

If conditions Then

VB expressions

Else

VB expressions

End If

* Any If...Then.. Else statement must end with End If. Sometime it is not necessary to use Else.

Example7.1 :

Private Sub OK_Click()

firstnum=Val(usernum1.Text)

secondnum=Val(usernum2.Text)

If total=firstnum+secondnum And Val(sum.Text)<>0 Then

    correct.Visible = True
   wrong.Visible = False
Else
    correct.Visible = False
    wrong.Visible = True
End If
End Sub

Example 7.2

In this example, the program will check whether the password entered by the user matches the password assigned by the Form_Load procedure. If the two passwords match, then the textbox will disappear and the label will display “Login Successful”; otherwise the label will display "Login Fail! Please enter your password again" and the user has to key in the password again.

Dim password As String

Private Sub Command1_Click()

If Text1.Text = password Then

Text1.Visible = False

Label1.Visible = True

Label1.Caption = "Login Successful"

Else

Label1.Visible = True

Label1.Caption = "Login Fail! Please enter your password again"

Text1.Text = ""

End If

End Sub

Private Sub Form_Load()

password = "1234"

End Sub

7.4 Nested If... Then...Else Statements

We need to use nested If...Then... Else statements if a condition is depending on other conditions that have to be fulfilled first. A nested If statements are enclosed within other If statements. There can be many levels of nested If .. Then ..Else statements but will examine only the two-level nested statements. The format for a two level nested If ..Then...else statement is as follows:

If condition A Then
   If Condition B Then
      VB6 statement
   Else
      VB6 statement
   End If
End If

* Any If...Then.. Else statement must end with End If. For two-level nested If, you must have two End If

Example 7.3

In this example, both conditions i.e. user name and password must be fulfilled before login can be sucessful.

Private Sub Command1_Click()
Dim userpassword, userName As String
userpassword = "123"
userName = "Liew"

If Text1.Text = userName Then

If Text2.Text = userpassword Then
MsgBox ("Login Successful")
Else
MsgBox ("Wrong password, login failed, please try again!")
End If

Else
MsgBox ("Wrong user name, login failed, please try again!")
End If

Example 7.4

In this example, suppose an airline company wish to recruit air stewards and air stewardesses, the height requirement might be at least 170 cm for male candidates and 160 for female candidates. The following code heps to filter the candidates based on gender and height.

If Option_Male.Value = True Then
    If Val(txtHeight.Text) >= 170 Then
        MsgBox ("Congratulation, welcome to join our team")
    Else
        MsgBox ("Sorry, your application is not sucessful,thank you.")
   End If

Else
   If Val(txtHeight.Text) >= 160 Then
       MsgBox ("Congratulation, welcome to join our team")
   Else
      MsgBox ("Sorry, your application is not sucessful,thank you.")
   End If
End If

View more examples that involve the usage of If......Then.... Else

Polling System	Choice Selection	Password Cracker
Dice	Reversi	Tic Tac Toe
Drag and Drop	Slot Machine	Library System

Lesson 8 : Select Case....End select Control Structure

In the previous lesson, we have learned how to control the program flow using the If...Then...ElseIf control structure. In this chapter, you will learn another way to control the program flow, that is, the Select Case control structure. However, the Select Case control structure is slightly different from the If....ElseIf control structure .

The difference is that the Select Case control structure can handle conditions with multiple outcomes in an easier manner than the If...Then...ElseIf control structure. If...Then...ElseIf control structure basically used to handle a single condition having more than two outcomes. Though If...Then...ElseIf control structure may also be used compute conditions with multiple outcomes, we need to use more than two levels of nested If...Then...ElseIf statements, this can make it difficult to read the codes. Therefore, the Select Case control structure is preferred when there exist many different conditions.

The format of the Select Case control structure is show below:

Select Case expression

   Case value1
        Block of one or more VB statements
   Case value2
        Block of one or more VB Statements
   Case value3
            .
        .
   Case Else
        Block of one or more VB Statements

End Select

Example 8.1

Dim grade As String

Private Sub Compute_Click( )

grade=txtgrade.Text

Select Case grade

Case "A"
result.Caption="High Distinction"

Case "A-"
result.Caption="Distinction"

Case "B"
result.Caption="Credit"

Case "C"
result.Caption="Pass"

Case Else
result.Caption="Fail"

End Select

End Sub

Example 8.2

Dim mark As Single

Private Sub Compute_Click()
'Examination Marks

mark = mrk.Text

Select Case mark

Case Is >= 85

comment.Caption = "Excellence"

Case Is >= 70

comment.Caption = "Good"

Case Is >= 60

comment.Caption = "Above Average"

Case Is >= 50

comment.Caption = "Average"

Case Else

comment.Caption = "Need to work harder"

End Select

End Sub

Example 8.3

Example 8.2 can be rewritten as follows:

Dim mark As Single

Private Sub Compute_Click()

'Examination Marks

mark = mrk.Text

Select Case mark

Case 0 to 49

comment.Caption = "Need to work harder"

Case 50 to 59

comment.Caption = "Average"

Case 60 to 69

comment.Caption = "Above Average"

Case 70 to 84

comment.Caption = "Good"

Case Else

comment.Caption = "Excellence"

End Select

End Sub

Lesson 9: Looping

In lesson 7 and lesson 8, we have learned how to handle decisions making process using If...Then...Else and also Select Case program structures in Visual Basic. Another procedure that involves decisions making is looping. Visual Basic allows a procedure to be repeated many times until a condition or a set of conditions is fulfilled. This is generally called looping . Looping is a very useful feature of Visual Basic because it makes repetitive works easier. There are two kinds of loops in Visual Basic, the Do...Loop and the For.......Next loop

9.1 Do Loop

The Do Loop statements have three different forms, as shown below:

a) Do While condition

Block of one or more VB statements

Loop

b)   Do
            Block of one or more VB statements
      Loop While condition

c)    Do Until condition
              Block of one or more VB statements
       Loop

d) Do
Block of one or more VB statements

Loop Until condition

Example 9.1

Do while counter <=1000

num.Text=counter

counter =counter+1

Loop

* The above example will keep on adding until counter >1000.

The above example can be rewritten as

num.Text=counter
counter=counter+1

Loop until counter>1000

9.2 Exiting the Loop

Sometime we need exit to exit a loop earlier when a certain condition is fulfilled. The keyword to use is Exit Do. You can examine Example 9.2 for its usage.

Example 9.2

Dim sum, n As Integer

Private Sub Form_Activate()

List1.AddItem "n" & vbTab & "sum"

n = n + 1

Sum = Sum + n

List1.AddItem n & vbTab & Sum

If n = 100 Then

Exit Do

End If

Loop

End Sub

Explanation

In the above example, we compute the summation of 1+2+3+4+……+100. In the design stage, you need to insert a ListBox into the form for displaying the output, named List1. The program uses the AddItem method to populate the ListBox. The statement List1.AddItem "n" & vbTab & "sum" will display the headings in the ListBox, where it uses the vbTab function to create a space between the headings n and sum.

9.3 For....Next Loop

The For....Next Loop event procedure is written as follows: For counter=startNumber to endNumber (Step increment) One or more VB statements Next	Example 9.3 b For counter=1 to 1000 step 10 counter=counter+1 Next
Example 9.3 a For counter=1 to 10 display.Text=counter Next	Example 9.3 c For counter=1000 to 5 step -5 counter=counter-10 Next

*Notice that the increment can be negative

Sometimes the user might want to get out from the loop before the whole repetitive process is executed, the command to use is Exit For. To exit a For….Next Loop, you can place the Exit For statement within the loop; and it is normally used together with the If…..Then… statement. Its usages is shown in Example 9.3 d.

Example 9.3 d

Private Sub Form_Activate( )

For n=1 to 10

If n>6 then

Exit For

End If

Else

Print n

End If

End Sub

9.4 Nested For...Next Loop

When you have a loop within a loop, then you have created a nested loop. You can actually have as many loops as you want in a nested loop provided the loops are not the never-ending type. For a nested loop that consists of two loops, the first cycle of the outer loop will be processed first, then it will process the whole repetitive process of the inner loop, then the second cycle of the outer loop will be processed and again the whole repetitive process of the inner loop will be processed. The program will end when the whole cycle of the outer loop is processed.

The Structure of a nested loop is :

For counter1=startNumber to endNumber (Step increment)

For counter2=startNumber to endNumber (Step increment)

One or more VB statements

Next counter2

Next counter1

Example 9.4

Private Sub Form_Activate ( )
    For firstCounter= 1to 5
        Print “Hello”
         For   secondCounter=1 to 4
             Print “Welcome to the VB tutorial”
        Next secondCounter
Next firstCounter
          Print” Thank you”
End Sub

Figure 9.1

The output of the above program is shown in Figure 9.1. As the outer loop has five repetitions, it will print the word “Hello” five times. Each time after it prints the word “Hello”, it will print four lines of the “Welcome to the VB tutorial” sentences as the inner loop has four repetitions.

9.5 The While….Wend Loop

The structure of a While….Wend Loop is very similar to the Do Loop. it takes the following form:

While condition

Statements

Wend

The above loop means that while the condition is not met, the loop will go on. The loop will end when the condition is met. Let’s examine the program listed in example 9.4.

Example 9.5

Dim sum, n As Integer

Private Sub Form_Activate()

List1.AddItem "n" & vbTab & "sum"

While n <> 100

n = n + 1

Sum = Sum + n

List1.AddItem n & vbTab & Sum

Wend

End Sub

Lesson 10: Introduction to VB Built-in Functions

A function is similar to a procedure but the main purpose of the function is to accept a certain input from the user and return a value which is passed on to the main program to finish the execution. There are two types of functions, the built-in functions (or internal functions) and the functions created by the programmers.

The general format of a function is
FunctionName (arguments)

The arguments are values that are passed on to the function.

In this lesson, you will learn two very basic but useful internal functions of Visual basic , i.e. the MsgBox( ) and InputBox ( ) functions.

10.1 MsgBox ( ) Function

The objective of MsgBox is to produce a pop-up message box that prompt the user to click on a command button before he /she can continues. This format is as follows:

yourMsg=MsgBox(Prompt, Style Value, Title)

The first argument, Prompt, will display the message in the message box. The Style Value will determine what type of command buttons appear on the message box, please refer Table 10.1 for types of command button displayed. The Title argument will display the title of the message board.

Table 10.1: Style Values

Style Value	Named Constant	Buttons Displayed
0	vbOkOnly	Ok button
1	vbOkCancel	Ok and Cancel buttons
2	vbAbortRetryIgnore	Abort, Retry and Ignore buttons.
3	vbYesNoCancel	Yes, No and Cancel buttons
4	vbYesNo	Yes and No buttons
5	vbRetryCancel	Retry and Cancel buttons

We can use named constant in place of integers for the second argument to make the programs more readable. In fact, VB6 will automatically shows up a list of names constant where you can select one of them.

Example: yourMsg=MsgBox( "Click OK to Proceed", 1, "Startup Menu")

and yourMsg=Msg("Click OK to Proceed". vbOkCancel,"Startup Menu")

are the same.

yourMsg is a variable that holds values that are returned by the MsgBox ( ) function. The values are determined by the type of buttons being clicked by the users. It has to be declared as Integer data type in the procedure or in the general declaration section. Table 10.2 shows the values, the corresponding named constant and buttons.

Table 10.2 : Return Values and Command Buttons

Value	Named Constant	Button Clicked
1	vbOk	Ok button
2	vbCancel	Cancel button
3	vbAbort	Abort button
4	vbRetry	Retry button
5	vbIgnore	Ignore button
6	vbYes	Yes button
7	vbNo	No button

Example 10.1

i. The Interface:

You draw three command buttons and a label as shown in Figure 10.1

Figure 10.1

ii. The procedure for the test button:

Private Sub Test_Click()
Dim testmsg As Integer
testmsg = MsgBox("Click to test", 1, "Test message")
If testmsg = 1 Then
Display.Caption = "Testing Successful"
Else
Display.Caption = "Testing fail"
End If
End Sub

When the user click on the test button, the image like the one shown in Figure 10.2 will appear. As the user click on the OK button, the message "Testing successful" will be displayed and when he/she clicks on the Cancel button, the message "Testing fail" will be displayed.

Figure 10.2

To make the message box looks more sophisticated, you can add an icon besides the message. There are four types of icons available in VB as shown in Table 10.3

Table 10.3

Value	Named Constant	Icon
16	vbCritical
32	vbQuestion
48	vbExclamation
64	vbInformation

Example 10.2

You draw the same Interface as in example 10.1 but modify the codes as follows:

Private Sub test2_Click()

Dim testMsg2 As Integer
testMsg2 = MsgBox("Click to Test", vbYesNoCancel + vbExclamation, "Test Message")
If testMsg2 = 6 Then
display2.Caption = "Testing successful"
ElseIf testMsg2 = 7 Then
display2.Caption = "Are you sure?"
Else
display2.Caption = "Testing fail"
End If

End Sub

In this example, the following message box will be displayed:

Figure 10.3

10.2 The InputBox( ) Function

An InputBox( ) function will display a message box where the user can enter a value or a message in the form of text. The format is

myMessage=InputBox(Prompt, Title, default_text, x-position, y-position)
myMessage is a variant data type but typically it is declared as string, which accept the message input by the users. The arguments are explained as follows:

Prompt - The message displayed normally as a question asked.
Title - The title of the Input Box.
default-text - The default text that appears in the input field where users can use it as his intended input or he may change to the message he wish to key in.
x-position and y-position - the position or the coordinate of the input box.

Example 10.3
i. The Interface

Figure 10.4

ii. The procedure for the OK button

Private Sub OK_Click()
Dim userMsg As String
userMsg = InputBox("What is your message?", "Message Entry Form", "Enter your messge here", 500, 700)
If userMsg <> "" Then
message.Caption = userMsg
Else
message.Caption = "No Message"
End If
End Sub
When a user click the OK button, the input box as shown in Figure 10.5 will appear. After user entering the message and click OK, the message will be displayed on the caption, if he click Cancel, "No message" will be displayed.

Lesson 11: Mathematical Functions

Custom Search

The mathematical functions are very useful and important in programming because very often we need to deal with mathematical concepts in programming such as chance and probability, variables, mathematical logics, calculations, coordinates, time intervals and etc. The common mathematical functions in Visual Basic are Rnd, Sqr, Int, Abs, Exp, Log, Sin, Cos, Tan , Atn, Fix and Round.

(i) Rnd is very useful when we deal with the concept of chance and probability. The Rnd function returns a random value between 0 and 1. In Example 1. When you run the program, you will get an output of 10 random numbers between 0 and 1. Randomize Timer is a vital statement here as it will randomize the process.

Example 1:

Private Sub Form_Activate

Randomize Timer

For x=1 to 10

Print Rnd

Next x

End Sub

The Output for example 1 is shown below:

Random numbers in their original forms are not very useful in programming until we convert them to integers. For example, if we need to obtain a random output of 6 random integers ranging from 1 to 6, which make the program behave as a virtual die, we need to convert the random numbers using the format Int(Rnd*6)+1. Let’s study the following example:

In this example, Int(Rnd*6) will generate a random integer between 0 and 5 because the function Int truncates the decimal part of the random number and returns an integer. After adding 1, you will get a random number between 1 and 6 every time you click the command button. For example, let say the random number generated is 0.98, after multiplying it by 6, it becomes 5.88, and using the integer function Int(5.88) will convert the number to 5; and after adding 1 you will get 6.

In this example, you place a command button and change its caption to ‘roll die’. You also need to insert a label into the form and clear its caption at the designing phase and make its font bigger and bold. Then set the border value to 1 so that it displays a border; and after that set the alignment to center. The statement Label1.Caption=Num means the integer generated will be displayed as the caption of the label.

Example 2:

Dim num as integer

Private Sub Command1_Click ( )

Randomize Timer

Num=Int(Rnd*6)+1

Label1.Caption=Num

End Sub

Now, run the program and then click on the roll die button, you will get an output like the figure below:

The Numeric Functions

The numeric functions are Int, Sqr, Abs, Exp, Fix, Round and Log.

a) Int is the function that converts a number into an integer by truncating its decimal part and the resulting integer is the largest integer that is smaller than the number. For example, Int(2.4)=2, Int(4.8)=4, Int(-4.6)= -5, Int(0.032)=0 and so on.

b) Sqr is the function that computes the square root of a number. For example, Sqr(4)=2, Sqr(9)=2 and etc.

c) Abs is the function that returns the absolute value of a number. So Abs(-8) = 8 and Abs(8)= 8.

d) Exp of a number x is the value of e^x. For example, Exp(1)=e¹ = 2.7182818284590

e) Fix and Int are the same if the number is a positive number as both truncate the decimal part of the number and return an integer. However, when the number is negative, it will return the smallest integer that is larger than the number. For example, Fix(-6.34)= -6 while Int(-6.34)=-7.

f) Round is the function that rounds up a number to a certain number of decimal places. The Format is Round (n, m) which means to round a number n to m decimal places. For example, Round (7.2567, 2) =7.26

g) Log is the function that returns the natural Logarithm of a number. For example,

Log 10= 2.302585

Example 3

This example computes the values of Int(x), Fix(x) and Round(x,n) in a table form. It uses the Do Loop statement and the Rnd function to generate 10 numbers. The statement x = Round (Rnd * 7, 7) rounds a random number between 0 and 7 to 7 decimal places. Using commas in between items will create spaces between them and hence a table of values can be created. The program and output are shown below

Private Sub Form_Activate ()

n = 1

Print " n", " x", "Int(x)", "Fix(x)", "Round(x, 4)"

Do While n < 11

Randomize Timer

x = Round (Rnd * 7, 7)

Print n, x, Int(x), Fix(x), Round(x, 4)

n = n + 1

Loop

End Sub

Lesson 12: Formatting Functions

Formatting output is a very important part of programming so that the data can be presented systematically and clearly to the users. Data in the previous lesson were presented fairly systematically through the use of commas and some of the functions like Int, Fix and Round. However, to have better control of the output format, we can use a number of formatting functions in Visual basic.

The three most common formatting functions in VB are Tab, Space, and Format

(i) The Tab function

Tab (n); x

The item x will be displayed at a position that is n spaces from the left border of the output form. There must be a semicolon in between Tab and the items you intend to display (VB will actually do it for you automatically).

Example 12.1

.Private Sub Form_Activate

Print "I"; Tab(5); "like"; Tab(10); "to"; Tab(15); "learn"; Tab(20); "VB"

Print Tab(10); "I"; Tab(15); "like"; Tab(20); "to"; Tab(25); "learn"; Tab(20); "VB"

Print Tab(15); "I"; Tab(20); ; "like"; Tab(25); "to"; Tab(30); "learn"; Tab(35); “VB"

End sub

The Output for example 1 is shown below:

(ii) The Space function

The Space function is very closely linked to the Tab function. However, there is a minor difference. While Tab (n) means the item is placed n spaces from the left border of the screen, the Space function specifies the number of spaces between two consecutive items. For example, the procedure

Example 12.2

Private Sub Form_Activate()

Print "Visual"; Space(10); "Basic"

End Sub

Means that the words Visual and Basic will be separated by 10 spaces

(iii) The Format function

The Format function is a very powerful formatting function which can display the numeric values in various forms. There are two types of Format function, one of them is the built-in or predefined format while another one can be defined by the users.

(a) The syntax of the predefined Format function is

Format (n, “style argument”)

where n is a number and the list of style arguments is shown in Table 12.1

Style argument	Explanation	Example
General Number	To display the number without having separators between thousands.	Format(8972.234, “General Number”)=8972.234
Fixed	To display the number without having separators between thousands and rounds it up to two decimal places.	Format(8972.2, “Fixed”)=8972.23
Standard	To display the number with separators or separators between thousands and rounds it up to two decimal places.	Format(6648972.265, “Standard”)= 6,648,972.27
Currency	To display the number with the dollar sign in front, has separators between thousands as well as rounding it up to two decimal places.	Format(6648972.265, “Currency”)= $6,648,972.27
Percent	Converts the number to the percentage form and displays a % sign and rounds it up to two decimal places.	Format(0.56324, “Percent”)=56.32 %

Table 12.1

Example 12.3

Private Sub Form_Activate()

Print Format (8972.234, "General Number")

Print Format (8972.2, "Fixed")

Print Format (6648972.265, "Standard")

Print Format (6648972.265, "Currency")

Print Format (0.56324, "Percent")

End Sub

Now, run the program and you will get an output like the figure below:

(b)

The syntax of the user-defined Format function is

Format (n, “user’s format”)

Although it is known as user-defined format, we still need to follows certain formatting styles. Examples of user-defined formatting style are listed in Table 12.2

Example	Explanation	Output
Format(781234.57,”0”)	Rounds to whole number without separators between thousands.	781235
Format(781234.57,”0.0”)	Rounds to 1 decimal place without separators between thousands.	781234.6
Format(781234.576,”0.00”)	Rounds to 2 decimal places without separators between thousands.	781234.58
Format(781234.576,”#,##0.00”)	Rounds to 2 decimal places with separators between thousands.	781,234.58
Format(781234.576,”$#,##0.00”)	Shows dollar sign and rounds to 2 decimal places with separators between thousands.	$781,234.58
Format(0.576,”0%”)	Converts to percentage form without decimal places.	58%
Format(0.5768,”0.00%”)	Converts to percentage form with 2 decimal places.	57.68%

Table 12.2

Example 12.4

Private Sub Form_Activate()
Print Format(781234.57, "0")
Print Format(781234.57, "0.0")
Print Format(781234.576, "0.00")
Print Format(781234.576, "#,##0.00")
Print Format(781234.576, "$#,##0.00")
Print Format(0.576, "0%")
Print Format(0.5768, "0.00%")
End Sub

The output is shown in the following figure:

Lesson 13: String Manipulation Functions

In this lesson, we will learn how to use some of the string manipulation function such as Len, Right, Left, Mid, Trim, Ltrim, Rtrim, Ucase, Lcase, Instr, Val, Str ,Chr and Asc.

(i)The Len Function

The length function returns an integer value which is the length of a phrase or a sentence, including the empty spaces. The format is

Len (“Phrase”)

For example,

Len (VisualBasic) = 11 and Len (welcome to VB tutorial) = 22

The Len function can also return the number of digits or memory locations of a number that is stored in the computer. For example,

Private sub Form_Activate ( )

X=sqr (16)

Y=1234

Z#=10#

Print Len(x), Len(y), and Len (z)

End Sub

will produce the output 1, 4 , 8. The reason why the last value is 8 is because z# is a double precision number and so it is allocated more memory spaces.

(ii) The Right Function

The Right function extracts the right portion of a phrase. The format is

Right (“Phrase”, n)

Where n is the starting position from the right of the phrase where the portion of the phrase is going to be extracted. For example,

Right(“Visual Basic”, 4) = asic

(iii)The Left Function

The Left$ function extract the left portion of a phrase. The format is

Left(“Phrase”, n)

Where n is the starting position from the left of the phase where the portion of the phrase is going to be extracted. For example,

Left (“Visual Basic”, 4) = Visu

(iv) The Ltrim Function

The Ltrim function trims the empty spaces of the left portion of the phrase. The format is

Ltrim(“Phrase”)

.For example,

Ltrim (“ Visual Basic”, 4)= Visual basic

(v) The Rtrim Function

The Rtrim function trims the empty spaces of the right portion of the phrase. The format is

Rtrim(“Phrase”)

.For example,

Rtrim (“Visual Basic ”, 4) = Visual basic

(vi) The Trim function

The Ttrim function trims the empty spaces on both side of the phrase. The format is

Trim(“Phrase”)

.For example,

Trim (“ Visual Basic ”) = Visual basic

(viii) The Mid Function

The Mid function extracts a substring from the original phrase or string. It takes the following format:

Mid(phrase, position, n)

Where position is the starting position of the phrase from which the extraction process will start and n is the number of characters to be extracted. For example,

Mid(“Visual Basic”, 3, 6) = ual Bas

(ix) The InStr function

The InStr function looks for a phrase that is embedded within the original phrase and returns the starting position of the embedded phrase. The format is

Instr (n, original phase, embedded phrase)

Where n is the position where the Instr function will begin to look for the embedded phrase. For example

Instr(1, “Visual Basic”,” Basic”)=8

(x) The Ucase and the Lcase functions

The Ucase function converts all the characters of a string to capital letters. On the other hand, the Lcase function converts all the characters of a string to small letters. For example,

Ucase(“Visual Basic”) =VISUAL BASiC

Lcase(“Visual Basic”) =visual basic

(xi) The Str and Val functions

The Str is the function that converts a number to a string while the Val function converts a string to a number. The two functions are important when we need to perform mathematical operations.

(xii) The Chr and the Asc functions

The Chr function returns the string that corresponds to an ASCII code while the Asc function converts an ASCII character or symbol to the corresponding ASCII code. ASCII stands for “American Standard Code for Information Interchange”. Altogether there are 255 ASCII codes and as many ASCII characters. Some of the characters may not be displayed as they may represent some actions such as the pressing of a key or produce a beep sound. The format of the Chr function is

Chr(charcode)

and the format of the Asc function is

Asc(Character)

The following are some examples:

Chr(65)=A, Chr(122)=z, Chr(37)=% , Asc(“B”)=66, Asc(“&”)=38

Lesson 14: Creating User-Defined Functions

14.1 Creating Your Own Function

The general format of a function is as follows:

Public Function functionName (Arg As dataType,..........) As dataType

Private Function functionName (Arg As dataType,..........) As dataType

* Public indicates that the function is applicable to the whole project and
Private indicates that the function is only applicable to a certain module or procedure.

Example 14.1

In this example, a user can calculate the future value of a certain amount of money he has today based on the interest rate and the number of years from now, supposing he will invest this amount of money somewhere .The calculation is based on the compound interest rate.

The code

Public Function FV(PV As Variant, i As Variant, n As Variant) As Variant

'Formula to calculate Future Value(FV)
'PV denotes Present Value
FV = PV * (1 + i / 100) ^ n

End Function

Private Sub compute_Click()

'This procedure will calculate Future Value
Dim FutureVal As Variant
Dim PresentVal As Variant
Dim interest As Variant
Dim period As Variant
PresentVal = PV.Text
interest = rate.Text
period = years.Text

'calling the funciton

FutureVal = FV(PresentVal, interest, period)
MsgBox ("The Future Value is " & FutureVal)

End Sub

Example 14.2

The following program will automatically compute examination grades based on the marks that a student obtained.

The Code

Public Function grade(mark As Variant) As String

Select Case mark
Case Is >= 80
grade = "A"
Case Is >= 70
grade = "B"
Case Is >= 60
grade = "C"
Case Is >= 50
grade = "D"
Case Is >= 40
grade = "E"
Case Else
grade = "F"
End Select

End Function

Private Sub compute_Click()

LblGrade.Caption = grade(TxtMark)

End Sub

Lesson 15: Creating VBA Functions For MS Excel

15.1 The Needs to Create VBA Functions in MS-Excel

You can create your own functions to supplement the built-in functions in Microsoft Excel spreadsheet, which are quite limited in some aspects. These user-defined functions are also called Visual Basic for Applications functions, or simply VBA functions. They are very useful and powerful if you know how to program them properly. One main reason we need to create user defined functions is to enable us to customize our spreadsheet environment for individual needs. For example, we might need a function that could calculate commissions payment based on the sales volume, which is quite difficult if not impossible by using the built-in functions alone.

Table 15.1: Commissions Payment Table

Sales Volume($)	Commissons
<500	3%
<1000	6%
<2000	9%
<5000	12%
>5000	15%

In table 15.1, when a salesman attains a sale volume of $6000, he will be paid $6000x15%=$720.00. A visual basic function to calculate the commissions can be written as follows:

Function Comm(Sales_V As Variant) as Variant

If Sales_V <500 Then
Comm=Sales_V*0.03
Elseif Sales_V>=500 and Sales_V<1000 Then
Comm=Sales_V*0.06
Elseif Sales_V>=1000 and Sales_V<2000 Then
Comm=Sales_V*0.09
Elseif Sales_V>=200 and Sales_V<5000 Then
Comm=Sales_V*0.12
Elseif Sales_V>=5000 Then
Comm=Sales_V*0.15
End If

End Function

15.2 Using Microsoft Excel Visual Basic Editor

To create VBA functions in MS Excel, you can click on tools, select macro and then click on Visual Basic Editor as shown in Figure 15.1

Figure 15.1: Inserting MS_Excel Visual Basic Editor

Upon clicking the Visual Basic Editor, the VB Editor windows will appear as shown in figure 15.2. To create a function, type in the function as illustrated in section 15.1 above After typing, save the file and then return to the Excel windows.

Figure 15.2 : The VB Editor

In the Excel window, type in the titles Sales Volume and Commissions in any two cells. By referring to figure 15.3, key-in the Comm function at cell C4 and by referencing the value in cell B4, using the format Comm(B4). Any value appear in cell B4 will pass the value to the Comm function in cell C4. For the rest of the rows, just copy the formula by dragging the bottom right corner of cell C4 to the required cells, a nice and neat table that shows the commissions will automatically appear (as shown in figure 15.3). It can also be updated anytime

Figure 15.3: MS Excel Windows- Sales Volume

Please refer to our Excel VBA Tutorial for a complete course on VBA for Excel

Lesson 16: Arrays

16.1 Introduction to Arrays

By definition, an array is a list of variables with the same data type and name. When we work with a single item, we only need to use one variable. However, if we have a list of items which are of similar type to deal with, we need to declare an array of variables instead of using a variable for each item

For example, if we need to enter one hundred names, it is difficulty to declare 100 different names, this is a waste of time and efforts. So, instead of declaring one hundred different variables, we need to declare only one array. We differentiate each item in the array by using subscript, the index value of each item, for example name(1), name(2),name(3) .......etc. , which will make declaring variables streamline and much more systematic.

16.2 Dimension of an Array

An array can be one dimensional or multidimensional. One dimensional array is like a list of items or a table that consists of one row of items or one column of items.

A two dimensional array is a table of items that make up of rows and columns. The format for a one dimensional array is ArrayName(x), the format for a two dimensional array is ArrayName(x,y) and a three dimensional array is ArrayName(x,y,z) . Normally it is sufficient to use one dimensional and two dimensional array ,you only need to use higher dimensional arrays if you need to deal with more complex problems. Let me illustrate the the arrays with tables.

Table 16.1. One dimensional Array

Student Name

Name(1)

Name(2)

Name(3)

Name(4)

Name(5)

Name(6)

Table 16.2 Two Dimensional Array

Name(1,1)	Name(1,2)	Name(1,3)	Name(1,4)
Name(2,1)	Name(2,2)	Name(2,3)	Name(2,4)
Name(3,1)	Name(3,2)	Name(3,3)	Name(3,4)

16.2 Declaring Arrays

We can use Public or Dim statement to declare an array just as the way we declare a single variable. The Public statement declares an array that can be used throughout an application while the Dim statement declare an array that could be used only in a local procedure.

The general format to declare a one dimensional array is as follow:

Dim arrayName(subs) as dataType

where subs indicates the last subscript in the array.

Example 16.1

Dim CusName(10) as String

will declare an array that consists of 10 elements if the statement Option Base 1 appear in the declaration area, starting from CusName(1) to CusName(10). Otherwise, there will be 11 elements in the array starting from CusName(0) through to CusName(10)

CusName(1)

CusName(2)

CusName(3)

CusName(4)

CusName(5)

CusName(6)

CusName(7)

CusName(8)

CusName(9)

CusName(10)

Example 16.2

Dim Count(100 to 500) as Integer

declares an array that consists of the first element starting from Count(100) and ends at Count(500)

The general format to declare a two dimensional array is as follow:

Dim ArrayName(Sub1,Sub2) as dataType

Example 16.3

Dim StudentName(10,10) will declare a 10x10 table make up of 100 students' Names, starting with StudentName(1,1) and end with StudentName(10,10).

16.3 Sample Programs

(i) Dim studentName(10) As String
Dim num As Integer
Private Sub addName()
For num = 1 To 10
studentName(num) = InputBox("Enter the student name", "Enter Name", "", 1500, 4500)
If studentName(num) <> "" Then
Form1.Print studentName(num)
Else
End
End If
Next
End Sub
The program accepts data entry through an input box and displays the entries in the form itself. As you can see, this program will only allows a user to enter 10 names each time he click on the start button.

ii) Dim studentName(10) As String
Dim num As Integer

Private Sub addName( )
For num = 1 To 10
studentName(num) = InputBox("Enter the student name")
List1.AddItem studentName(num)
Next
End Sub
Private Sub Start_Click()
addName
End Sub
The program accepts data entries through an InputBox and displays the items in a list box.

Lesson 17: Working with Files

17.1 Introduction

Up until lesson 13 we are only creating programs that could accept data at runtime, the data disappears when the program terminates . Is it possible to save the data into a storage device, such as a hard disk , DVDR or pendrive? The answer is YES. In this chapter, we shall learn how to create files by writing them into a storage device and then retrieve the data by reading the contents of the files using a customized VB program.

17.2 Creating a File

To create a file , we use the following command

Open "fileName" For Output As #fileNumber

Each file created must have a file name and a file number for identification. As for the file name, you must also specify the path where the file will reside.

Examples:

Open "c:\My Documents\sample.txt" For Output As #1

will create a text file by the name of sample.txt in My Document folder in C drive. The accompanied file number is 1. If you wish to create and save the file in A drive, simply change the path, as follows"

Open "A:\sample.txt" For Output As #1

or If you wish to create a HTML file , simply change the extension to .html

Open "c:\My Documents\sample.html" For Output As # 2

17.2.1 Sample Program : Creating a text file

Private Sub create_Click()
Dim intMsg As String
Dim StudentName As String
Open "c:\My Documents\sample.txt" For Output As #1
intMsg = MsgBox("File sample.txt opened")
StudentName = InputBox("Enter the student Name")
Print #1, StudentName
intMsg = MsgBox("Writing a" & StudentName & " to sample.txt ")
Close #1
intMsg = MsgBox("File sample.txt closed")
End Sub

* The above program will create a file sample.txt in the My Documents folder and ready to receive input from users. Any data input by the user will be saved in this text file.

17.3 Reading a file

To read a file created in section 17.2, you can use the input # statement. However, we can only read the file according to the format when it was written. You have to open the file according to its file number and the variable that hold the data. We also need to declare the variable using the DIM command.

17.3.1 Sample Program: Reading file
Private Sub Reading_Click()
Dim variable1 As String
Open "c:\My Documents\sample.txt" For Input As #1
Input #1, variable1
Text1.Text = variable1
Close #1
End Sub
* This program will open the sample.txt file and display its contents in the Text1 textbox.

Example 17.3.2 Creating and Reading files using Common Dialog Box

This example uses the common dialog box to create and read the text file, which is
much easier than the previous examples.Many operations are handled by the
common dialog box. The following is the program:

Dim linetext As String
Private Sub open_Click()
CommonDialog1.Filter = "Text files{*.txt)|*.txt"
CommonDialog1.ShowOpen

If CommonDialog1.FileName <> "" Then
Open CommonDialog1.FileName For Input As #1
Do
Input #1, linetext
Text1.Text = Text1.Text & linetext
Loop Until EOF(1)
End If
Close #1
End Sub
Private Sub save_Click()
CommonDialog1.Filter = "Text files{*.txt)|*.txt"
CommonDialog1.ShowSave
If CommonDialog1.FileName <> "" Then
Open CommonDialog1.FileName For Output As #1
Print #1, Text1.Text
Close #1
End If
End Sub

The syntax CommonDialog1.Filter = "Text files{*.txt)|*.txt"ensures that only the textfile is read or saved .The statement CommonDialog1.ShowOpen is to display the open file dialog box and the statement CommonDialog1.ShowSave is to display the save file dialog box. Text1.Text = Text1.Text & linetext is to read the data and display them in the Text1 textbox

The Output window is shown below:

Lesson 18: Graphics

Graphics is a very important part of visual basic programming because an attractive interface will be appealing to the users. In the old BASIC, drawing and designing graphics are considered difficult jobs, as they have to be programmed line by line in a text-based environment. However, in Visual Basic 6, these jobs have been made easy. There are four basic controls in VB6 that you can use to draw graphics on your form: the line control, the shape control, the image box and the picture box

18.1The line and Shape controls

To draw a straight line, just click on the line control and then use your mouse to draw the line on the form. After drawing the line, you can then change its color, width and style using the BorderColor, BorderWidth and BorderStyle properties.Similarly, to draw a shape, just click on the shape control and draw the shape on the form. The default shape is a rectangle, with the default shape property set at 0. You can change the shape to square, oval, circle and rounded rectangle by changing the shape property’s value to 1, 2, 3 , 4, and 5 respectively. In addition, you can change its background color using the BackColor property, its border style using the BorderStyle property, its border color using the BorderColor pproperty as well its border width using the BorderWidth property.

Example 18.1

The program in this example allows the user to change the shape by selecting a particular shape from a list of options from a list box, as well as changing its color through a common dialog box.

The objects to be inserted in the form are a list box, a command button, a shape control and a common dialog box. The common dialog box can be inserted by clicking on ‘project’ on the menu and then select the Microsoft Common Dialog Control 6.0 by clicking the check box. After that, the Microsoft Common Dialog Control 6.0 will appear in the toolbox; and you can drag it into the form. The list of items can be added to the list box through the AddItem method. The procedure for the common dialog box to present the standard colors is as follows:

CommonDialog1.Flags = &H1&

CommonDialog1.ShowColor

Shape1.BackColor = CommonDialog1.Color

The last line will change the background color of the shape by clicking on a particular color on the common dialog box as shown in the Figure 18.1 below:

The Interface.

Figure 18.1

The color dialog box

The Code

Private Sub Form_Load()

List1.AddItem "Rectangle"

List1.AddItem "Square"

List1.AddItem "Oval"

List1.AddItem "Circle"

List1.AddItem "Rounded Rectangle"

List1.AddItem "Rounded Square"

End Sub

Private Sub List1_Click()

Select Case List1.ListIndex

Case 0

Shape1.Shape = 0

Case 1

Shape1.Shape = 1

Case 2

Shape1.Shape = 2

Case 3

Shape1.Shape = 3

Case 4

Shape1.Shape = 4

Case 5

Shape1.Shape = 5

End Select

End Sub

Private Sub Command1_Click()

CommonDialog1.Flags = &H1&

CommonDialog1.ShowColor

Shape1.BackColor = CommonDialog1.Color

End Sub

18.2 The Image Box and the Picture Box

Using the line and shape controls to draw graphics will only enable you to create a simple design. In order to improve the look of the interface, you need to put in images and pictures of your own. Fortunately, there are two very powerful graphics tools you can use in Visual Basic 6 which are the image box and the picture box.

To load a picture or image into an image box or a picture box, you can click on the picture property in the properties window to launch a dialog box that will prompt you to select a certain picture file. You can also load a picture at runtime by using the LoadPictrure ( ) method. The syntax is

Image1.Picture= LoadPicture("C:\path name\picture file name") or

picture1.Picture= LoadPicture("C:\path name\picture name")

For example, the following statement will load the grape.gif picture into the image box.

Image1.Picture= LoadPicture("C:\My Folder\VB program\Images\grape.gif")

Example 18.2

In this example, each time you click on the ‘change pictures’ button as shown in Figure 18.2, you will be able to see three images loaded into the image boxes. This program uses the Rnd function to generate random integers and then uses the LoadPicture method to load different pictures into the image boxes using the If…Then…Statements based on the random numbers generated.

Figure 18.2

The code for Example 18.2

Dim a, b, c As Integer

Private Sub Command1_Click ()

Randomize Timer

a = 3 + Int(Rnd * 3)

b = 3 + Int(Rnd * 3)

c = 3 + Int(Rnd * 3)

If a = 3 Then

Image1(0).Picture = LoadPicture("C:\My Folder\VB program\Images\grape.gif")

End If

If a = 4 Then

Image1(0).Picture = LoadPicture("C:\My Folder\VB program\Images\cherry.gif")

End If

If a = 5 Then

Image1(0).Picture = LoadPicture("C:\My Folder\VB program\Images\orange.gif")

End If

If b = 3 Then

Image1(1).Picture = LoadPicture("C:\My Folder\VB program\Images\grape.gif")

End If

If b = 4 Then

Image1(1).Picture = LoadPicture("C:\My Folder\VB program\Images\cherry.gif")

End If

If b = 5 Then

Image1(1).Picture = LoadPicture("C:\My Folder\VB program\Images\orange.gif")

End If

If c = 3 Then

Image1(2).Picture = LoadPicture("C:\My Folder\VB program\Images\grape.gif")

End If

If c = 4 Then

Image1(2).Picture = LoadPicture("C:\My Folder\VB program\Images\cherry.gif")

End If

If c = 5 Then

Image1(2).Picture = LoadPicture("C:\My Folder\VB program\Images\orange.gif")

End If

End Sub

18.3 PSet, Line and Circle Drawing Methods

Other than using the line and shape controls to draw graphics on the form, you can also use the Pset, Line and Circle methods to draw graphics on the form.

(a) The Pset Method

The Pset method draw a dot on the screen, it takes the format

Pset (x , y ), color

(x,y) is the coordinates of the point and color is its color. To specify the color, you can use the color codes or the standard VB color constant such as VbRed, VbBlue, VbGeen and etc. For example, Pset(100,200), VbRed will display a red dot at the (100,200) coordinates.

The Pset method can also be used to draw a straight line on the form. The procedure is

For x= a to b

Pset(x,x)

Next x

This procedure will draw a line starting from the point (a,a) and to the point (b,b). For example, the following procedure will draw a magenta line from the point (0,0) to the point (1000,1000).

For x= 0 to 100

Pset(x,x) , vbMagenta

Next x

(b) The Line Method

Although the Pset method can be used to draw a straight line on the form, it is a little slow. It is better to use the Line method if you want to draw a straight line faster. The format of the Line command is shown below. It draws a line from the point (x1, y1) to the point (x2, y2) and the color constant will determine the color of the line.

Line (x1, y1)-(x2, y2), color

For example, the following command will draw a red line from the point (0, 0) to the point (1000, 2000).

Line (0, 0)-(1000, 2000), VbRed

The Line method can also be used to draw a rectangle. The format is

Line (x1-y1)-(x2, y2), color, B

The four corners of the rectangle are (x1-y1), (x2-y1), (x1-y2) and (x2, y2)

Another variation of the Line method is to fill the rectangle with a certain color. The format is

Line (x1, y1)-(x2, y2), color, BF

If you wish to draw the graphics in a picture box, you can use the following formats

· Picture1.Line (x1, y1)-(x2, y2), color

· Picture1.Line (x1-y1)-(x2, y2), color, B

· Picture1.Line (x1-y1)-(x2, y2), color, BF

· Picture1.Circle (x1, y1), radius, color

(c) The Circle Method

The circle method takes the following format

Circle (x1, y1), radius, color

That draws a circle centered at (x1, y1), with a certain radius and a certain border color. For example, the procedure

Circle (400, 400), 500, VbRed

draws a circle centered at (400, 400) with a radius of 500 twips and a red border.

Example: Please refer to the Drawing Program

Lesson 19: Creating Multimedia Applications-Part I

You can create various multimedia applications in VB that could play audio CD, audiofiles, VCD , video files and more. To be able to play multimedia files or multimedia devices, you have to insert Microsoft Multimedia Control into your VB applications that you are going to create. However, Microsoft Multimedia Control is not normally included in the startup toolbox, therefore you need to add the MM control by pressing Ctrl+T and select it from the components dialog box that is displayed.

19.1 Creating a CD player

In this program, you can create a CD player that resembles an actual CD player. It allows the user select a track to play, to fast forward, to rewind and also to eject the CD. It can also display the track being played. The interface and code are shown below.

a) The Interface.

The Code

Private Sub Form_Load()
'To position the page at the center
Left = (Screen.Width - Width) \ 2
Top = (Screen.Height - Height) \ 2
'Initialize the CD
myCD.Command = "Open"

End Sub

Private Sub myCD_StatusUpdate()

'Update the track number
trackNum.Caption = myCD.Track
End Sub

Private Sub Next_Click()
myCD.Command = "Next"
End Sub

Private Sub Play_Click()
myCD.Command = "Play"

End Sub

Private Sub Previous_Click()
myCD.Command = "Prev"
End Sub

Private Sub Stop_Click()
myCD.Command = "Stop"
End Sub

Lesson 20: Creating Multimedia Applications-Part II

In previous lesson, we have programmed a CD player. Now, by making some modifications, you canl transform the CD player into an audio player. This player will be created in such a way that it could search for wave and midi files in your drives and play them.

In this project, you need to insert a ComboBox, a DriveListBox, a DirListBox, a TextBox and aFileListBox into your form. I Shall briefly discuss the function of each of the above controls. Besides, you must also insert Microsoft Multimedia Control(MMControl) into your form , you may make it visible or invisible. In my program, I choose to make it invisible so that I can use the command buttons created to control the player.

ComboBox- to display and enable selection of different type of files.
DriveListBox- to allow selection selection of different drives available on your PC.
DirListBox - To display directories
TextBox - To display selected files
FileListBox- To display files that are available

Relevant code must be written to coordinate all the above controls so that the application can work properly. The program should follow in the following logical way:

Step 1: User chooses the type of files he wants to play.

Step2:User selects the drive that might contains the relevant audio files.

Step 3:User looks into directories and subdirectories for the files specified in step1. The files should be displayed in the FileListBox.

Step 4: User selects the files from the FileListBox and click the Play button.

Step 5: User clicks on the Stop button to stop playing and Exit button to end the application.

The Interface
The Code Private Sub Combo1_Change() ' to determine file type If ListIndex = 0 Then File1.Pattern = (".wav") ElseIf ListIndex = 1 Then File1.Pattern = (".mid") Else Fiel1.Pattern = (".") End If End Sub 　 Private Sub Dir1_Change() 'To change directories and subdirectories(or folders and subfolders) File1.Path = Dir1.Path If Combo1.ListIndex = 0 Then File1.Pattern = (".wav") ElseIf Combo1.ListIndex = 1 Then File1.Pattern = (".mid") Else File1.Pattern = (".") End If End Sub	Private Sub play_Click() 'To play WaveAudio file or Midi File Command2_Click If Combo1.ListIndex = 0 Then AudioPlayer.DeviceType = "WaveAudio" ElseIf Combo1.ListIndex = 1 Then AudioPlayer.DeviceType = "Sequencer" End If AudioPlayer.FileName = Text1.Text AudioPlayer.Command = "Open" AudioPlayer.Command = "Play" 　 End Sub Private Sub stop_Click() If AudioPlayer.Mode = 524 Then Exit Sub If AudioPlayer.Mode <> 525 Then AudioPlayer.Wait = True AudioPlayer.Command = "Stop" End If AudioPlayer.Wait = True AudioPlayer.Command = "Close" End Sub
Private Sub Drive1_Change() 'To change drives Dir1.Path = Drive1.Drive End Sub Private Sub File1_Click() If Combo1.ListIndex = 0 Then File1.Pattern = (".wav") ElseIf Combo1.ListIndex = 1 Then File1.Pattern = (".mid") Else File1.Pattern = (".") End If If Right(File1.Path, 1) <> "\" Then filenam = File1.Path + "\" + File1.FileName Else filenam = File1.Path + File1.FileName End If Text1.Text = filenam End Sub Private Sub Form_Load() 'To center the Audioplayer startup page Left = (Screen.Width - Width) \ 2 Top = (Screen.Height - Height) \ 2 Combo1.Text = ".wav" Combo1.AddItem ".wav" Combo1.AddItem "*.mid" Combo1.AddItem "All files" End Sub

Lesson 21: Creating Multimedia Applications-Part III

In lesson 20, we have created an audio player. Now, by making further modifications, you can transform the audio player into a picture viewer. This viewer will be created in such a way that it could search for all types of graphics files in your drives and displays them in a picture frame.

Similar to the previous project, in this project, you need to insert a ComboBox, a DriveListBox, a DirListBox, a TextBox and a FileListBox into your form. I Shall briefly explain again the function of each of the above controls.

· ComboBox- to display and enable selection of different type of files.

· DriveListBox- to allow selection of different drives available on your PC.

· DirListBox - To display directories

· TextBox - To display selected files

· FileListBox- To display files that are available

Relevant code must be written to coordinate all the above controls so that the application can work properly. The program should flow in the following logical way:

Step 1: The user chooses the type of files he wants to play.

Step2:The user selects the drive that might contains the relevant graphic files.

Step 3:The user looks into directories and subdirectories for the files specified in step1. The files should be displayed in the FileListBox.

Step 4: The user selects the files from the FileListBox and click the Show button.

Step 5: The user clicks on Exit button to end the application.

The Interface

The Code
Private Sub Form_Load()
'To center the player
Left = (Screen.Width - Width) \ 2
Top = (Screen.Height - Height)\2

Combo1.Text = "All graphic files"
Combo1.AddItem "All graphic files"
Combo1.AddItem "All files"
End Sub
　
Private Sub Combo1_Change()
If ListIndex = 0 Then
File1.Pattern = ("*.bmp;*.wmf;*.jpg;*.gif")
Else
Fiel1.Pattern = ("*.*")
End If
End Sub
'Specific the types of files to load
Private Sub Dir1_Change()
File1.Path = Dir1.Path
File1.Pattern = ("*.bmp;*.wmf;*.jpg;*.gif")
End Sub
'Changing Drives
Private Sub Drive1_Change()
Dir1.Path = Drive1.Drive
End Sub ---------> Continue on the right

Private Sub File1_Click()

If Combo1.ListIndex = 0 Then
File1.Pattern = ("*.bmp;*.wmf;*.jpg;*.gif")
Else
File1.Pattern = ("*.*")
EnId If

If Right(File1.Path, 1) <> "\" Then
filenam = File1.Path + "\" + File1.FileName
Else
filenam = File1.Path + File1.FileName
End If
Text1.Text = filenam
End Sub

Private Sub show_Click()
If Right(File1.Path, 1) <> "\" Then
filenam = File1.Path + "\" + File1.FileName
Else
filenam = File1.Path + File1.FileName
End If
'To load the picture into the picture box
picture1.Picture = LoadPicture(filenam)
End Sub
　

Lesson 22: Creating Multimedia Applications-Part IV:

A Multimedia Player

In lesson 20, we have created an audio player. Now, by making more modifications, you can transform the audio player into a multimedia player. This player will be able to search for all types of video files and audio files in your drives and play them. In this project, you will need to insert a ComboBox, aDriveListBox, a DirListBox, a TextBox ,a FileListBox and a PictureBox into your form.

We Shall briefly explain the function of each of the above controls.

· ComboBox- to display and enable selection of different type of files.

· DriveListBox- to display different drives available on your PC.

· DirListBox - To display the directories in your drives

· TextBox - To display selected files

· FileListBox- To display files that are available

· PictureBox- To play the video files

Besides, you must also insert the Microsoft Multimedia Control(MMControl) into your form , you may make it visible or invisible. In our program, we choose to make it invisible so that we can use the command buttons created to control the player.In order to search for a multimedia file and play it with the multimedia player, the user needs to carry out the following steps:

Step 1: Decide the type of files he or she wants to play.

Step2: Select the drive that might contains the relevant multimedia files.

Step 3: Look into directories and subdirectories for the files specified in step1. The files should be displayed in the FileListBox.

Step 4: Select the files from the FileListBox and clicks the Play button.

Step 5: Click on the Stop button to stop playing and Exit button to end the application.

The Interface

The Code

Private Sub Form_Load()

'To fix the player size
Left = (Screen.Width - Width) \ 2
Top = (Screen.Height - Height) \ 2
Combo1.Text = "*.wav"
Combo1.AddItem "*.wav"
Combo1.AddItem "*.mid"
Combo1.AddItem "*.avi;*.mpg"
Combo1.AddItem "All files"

End Sub

Private Sub Combo1_Change()

'To select types of media files

If ListIndex = 0 Then
File1.Pattern = ("*.wav")
ElseIf ListIndex = 1 Then
File1.Pattern = ("*.mid")
ElseIf ListIndex = 2 Then
File1.Pattern = ("*.avi;*.mpg")
Else
Fiel1.Pattern = ("*.*")
End If

End Sub

Private Sub Dir1_Change()

'To search the directories or folders for the media files

File1.Path = Dir1.Path
If Combo1.ListIndex = 0 Then
File1.Pattern = ("*.wav")
ElseIf Combo1.ListIndex = 1 Then
File1.Pattern = ("*.mid")
ElseIf Combo1.ListIndex = 2 Then
File1.Pattern = ("*.avi;*.mpg")
Else
File1.Pattern = ("*.*")
End If

End Sub

Private Sub Drive1_Change()

'To Change Drives

Dir1.Path = Drive1.Drive

End Sub

Private Sub File1_Click()

'To load the selected file

If Combo1.ListIndex = 0 Then
File1.Pattern = ("*.wav")
ElseIf Combo1.ListIndex = 1 Then
File1.Pattern = ("*.mid")
ElseIf Combo1.ListIndex = 2 Then
File1.Pattern = ("*.avi;*.mpg")
Else
File1.Pattern = ("*.*")
End If

If Right(File1.Path, 1) <> "\" Then
filenam = File1.Path + "\" + File1.FileName
Else
filenam = File1.Path + File1.FileName
End If
Text1.Text = filenam

End Sub

Private Sub play_Click()

MMPlayer.FileName = Text1.Text
MMPlayer.Command = "Open"
MMPlayer.Command = "Play"
MMPlayer.hWndDisplay = videoscreen.hWnd

End Sub

Private Sub stop_Click()

If MMPlayer.Mode = 524 Then Exit Sub
If MMPlayer.Mode <> 525 Then
MMPlayer.Wait = True
MMPlayer.Command = "Stop"
End If
MMPlayer.Wait = True
MMPlayer.Command = "Close"

End Sub

Lesson 23: Creating database applications in VB-Part I

Visual basic allows us to manage databases created with different database programs such as MS Access, Dbase, Paradox and etc. In this lesson, we are not dealing with how to create database files but we will see how we can access database files in the VB environment.

In the following example, we will create a simple database application which enable one to browse customers' names. To create this application, insert the data control into the new form. Place the data control somewhere at the bottom of the form. Name the data control as data_navigator. To be able to use the data control, we need to connect it to a database. We can create a database file using any database application but I suggest we use the database files that come with VB6. Let selectNWIND.MDB as our database file.　

To connect the data control to this database, double-click the DatabaseName property in the properties window and select NWIND.MDB. Next, double-click on the RecordSource property to select the customers table from the database. You can also change the caption of the data control to anything , we use "Click to browse Customers" . After that, we place a label and change its caption to Customer Name. Finally, insert another label and name it as cus_name and leave the label empty as customers' names will appear here when we click the arrows on the data control.

Next, We need to bind this label to the data control for the application to work. To do this, open the label's DataSource and select data_navigator that will appear automatically. One more thing that we need to do is to bind the label to the correct field so that data in this field will appear on this label. To do this, open the DataField property and select ContactName. Now, press F5 and run the program. You should be able to browse all the customers' names by clicking the arrows on the data control.

The Design Interface.

The Runtime Interface

You can also add other fields using exactly the same method. For example, you can add adress, city and telephone number to the database browser.

Lesson 24: Creating database applications in VB-Part II

In Lesson 23, you have learned how to create a simple database application using data control. In this lesson, you will work on the same application but use some slightly more advance commands. The data control support some methods that are useful in manipulating the database, for example, to move the pointer to a certain location. The following are some of the commands that you can use to move the pointer around:

' Move to the first record

data1.RecordSet.MoveFirst

' Move to the last record

data1.RecordSet.MoveLast

' Move to the next record

data1.RecordSet.MoveNext

' Move to the first record

data1.RecordSet.Previous

You can also add, save and delete records using the following commands:

data1.RecordSet.AddNew ' Adds a new record

data1.RecordSet.Update ' Updates and saves the new record

data1.RecordSet.Delete ' Deletes a current record

*note: data1 is the name of data control

In the following example, you shall insert four commands and label them as First Record, Next Record, Previous Record and Last Record . They will be used to navigator around the database without using the data control. You still need to retain the same data control (from example in lesson 19) but set the property Visible to no so that users will not see the data control but use the button to browse through the database instead. Now, double-click on the command button and key in the codes according to the labels.

Private Sub Command1_Click()
data1.Recordset.MoveFirst
End Sub

Private Sub Command2_Click()
data1.Recordset.MoveNext
End Sub

Private Sub Command3_Click()
data1.Recordset.MovePrevious
End Sub

Private Sub Command4_Click()
data1.Recordset.MoveLast
End Sub

　

Run the application and you shall obtain the interface below and you will be able to browse the database using the four command buttons.

Lesson 25: Creating VB database applications using ADO control

In Lesson 22 and Lesson 23, we have learned how to build VB database applications using data control. However, data control is not a very flexible tool as it could only work with limited kinds of data and must work strictly in the Visual Basic environment.

To overcome these limitations, we can use a much more powerful data control in Visual Basic, known as ADO control. ADO stands for ActiveX data objects. As ADO is ActiveX-based, it can work in different platforms (different computer systems) and different programming languages. Besides, it can access many different kinds of data such as data displayed in the Internet browsers, email text and even graphics other than the usual relational and non relational database information.

To be able to use ADO data control, you need to insert it into the toolbox. To do this, simply press Ctrl+T to open the components dialog box and select Microsoft ActiveX Data Control 6. After this, you can proceed to build your ADO-based VB database applications.

The following example will illustrate how to build a relatively powerful database application using ADO data control. First of all, name the new form as frmBookTitle and change its caption to Book Titles- ADO Application. Secondly, insert the ADO data control and name it asadoBooks and change its caption to book. Next, insert the necessary labels, text boxes and command buttons. The runtime interface of this program is shown in the diagram below, it allows adding and deletion as well as updating and browsing of data.

The property settings of all the controls are listed as follow:

Control Property	Setting
Form Name	frmBookTitle
Form Caption	Book Titles -ADOApplication
ADO Name	adoBooks
Label1 Name	lblApp
Label1 Caption	Book Titles
Label 2 Name	lblTitle
Label2 Caption	Title :
Label3 Name	lblYear
Label3 Caption	Year Published:
Label4 Name	lblISBN
Label4 Caption	ISBN:
Labe5 Name	lblPubID
Label5 Caption	Publisher's ID:
Label6 Name	lblSubject
Label6 Caption	Subject :
TextBox1 Name	txtitle
TextBox1 DataField	Title
TextBox1 DataSource	adoBooks
TextBox2 Name	txtPub
TextBox2 DataField	Year Published
TextBox2 DataSource	adoBooks
TextBox3 Name	txtISBN
TextBox3 DataField	ISBN
TextBox3 DataSource	adoBooks
TextBox4 Name	txtPubID
TextBox4 DataField	PubID
TextBox4 DataSource	adoBooks
TextBox5 Name	txtSubject
TextBox5 DataField	Subject
TextBox5 DataSource	adoBooks
Command Button1 Name	cmdSave
Command Button1 Caption	&Save
Command Button2 Name	cmdAdd
Command Button2 Caption	&Add
Command Button3 Name	cmdDelete
Command Button3 Caption	&Delete
Command Button4 Name	cmdCancel
Command Button4 Caption	&Cancel
Command Button5 Name	cmdPrev
Command Button5 Caption	&<
Command Button6 Name	cmdNext
Command Button6 Caption	&>
Command Button7 Name	cmdExit
Command Button7 Caption	E&xit

To be able to access and manage a database, you need to connect the ADO data control to a database file. We are going to useBIBLIO.MDB that comes with VB6. To connect ADO to this database file , follow the steps below:

a) Click on the ADO control on the form and open up the properties window.

b) Click on the ConnectionString property, the following dialog box will appear.

when the dialog box appear, select the Use Connection String's Option. Next, click build and at the Data Link dialog box, double-Click the option labeled Microsoft Jet 3.51 OLE DB provider.

After that, click the Next button to select the file BIBLO.MDB. You can click on Text Connection to ensure proper connection of the database file. Click OK to finish the connection.

Finally, click on the RecordSource property and set the command type to adCmd Table and Table name to Titles. Now you are ready to use the database file.

Now, you need to write code for all the command buttons. After which, you can make the ADO control invisible.

For the Save button, the program codes are as follow:

Private Sub cmdSave_Click()

adoBooks.Recordset.Fields("Title") = txtTitle.Text
adoBooks.Recordset.Fields("Year Published") = txtPub.Text
adoBooks.Recordset.Fields("ISBN") = txtISBN.Text
adoBooks.Recordset.Fields("PubID") = txtPubID.Text
adoBooks.Recordset.Fields("Subject") = txtSubject.Text
adoBooks.Recordset.Update

End Sub

For the Add button, the program codes are as follow:

Private Sub cmdAdd_Click()

adoBooks.Recordset.AddNew

End Sub

For the Delete button, the program codes are as follow:

Private Sub cmdDelete_Click()

Confirm = MsgBox("Are you sure you want to delete this record?", vbYesNo, "Deletion Confirmation")
If Confirm = vbYes Then
adoBooks.Recordset.Delete
MsgBox "Record Deleted!", , "Message"
Else
MsgBox "Record Not Deleted!", , "Message"
End If

End Sub
　

For the Cancel button, the program codes are as follow:

Private Sub cmdCancel_Click()

txtTitle.Text = ""
txtPub.Text = ""
txtPubID.Text = ""
txtISBN.Text = ""
txtSubject.Text = ""

End Sub

For the Previous (<) button, the program codes are

Private Sub cmdPrev_Click()

If Not adoBooks.Recordset.BOF Then
adoBooks.Recordset.MovePrevious
If adoBooks.Recordset.BOF Then
adoBooks.Recordset.MoveNext
End If
End If

End Sub

For the Next(>) button, the program codes are

Private Sub cmdNext_Click()

If Not adoBooks.Recordset.EOF Then
adoBooks.Recordset.MoveNext
If adoBooks.Recordset.EOF Then
adoBooks.Recordset.MovePrevious
End If
End If

End Sub

Click here to view a related sample program

Lesson 26: Using Microsoft DataGrid Control 6.0

In the previous lesson, we use textboxes to display data by connecting them to a database via Microsoft ADO data Control 6.0. The textbox is not the only control that can display data from a database, many other controls in Visual Basic can display data. One of the them is the DataGrid control. DataGrid control can be used to display the entire table of a recordset of a database. It allows users to view and edit data.

DataGrid control is the not the default item in the Visual Basic control toolbox, you have to add it from the VB6 components. To add the DataGrid control, click on the project on the menu bar and select components to access the dialog box that displays all the available VB6 components, as shown in the diagram below. Select Microsoft DataGrid Control 6.0 by clicking the checkbox beside this item. Before you exit the dialog box, you also need to select the Microsoft ADO data control so that you are able to access the database. Last, click on the OK button to exit the dialog box. Now you should be able to see that the DataGrid control and the ADO data control are added to the toolbox. The next step is to drag the DataGrid control and the ADO data control into the form.

The components dialog box is shown below:

Before you proceed , you need to create a database file using Microsoft Access. Here we created a file to store the information of my books and we named the table book. After creating the table, enter a few records, as shown in the table below:

Next, you need to connect the database to the ADO data control. To do that, right click on the ADO data control and select theADODC properties, the following dialog box will appear.

Next click on the Build button and the Data Link Properties dialog box will appear (as shown below). In this dialog box, select the database file you have created, in my case, the file name is books.mdb. Press test connection to see whether the connection is successful. If the connection is successful, click OK to return to the ADODC property pages dialog box. At the ADODC property pages dialog box, click on the Recordsource tab and select 2-adCmdTable under command type and select book as the table name, then click OK.

Finally you need to display the data in the DataGrid control. To accomplish this, go to the properties window and set the DataSource property of the DataGrid to Adodc1. You can also permit the user to add and edit your records by setting the AllowUpdate property to True. If you set this property to false, the user cannot edit the records. Now run the program and the output window is shown below:

Lesson 27: Using SQL queries in Visual Basic 6

In the previous chapter, we have learned to use the DataGrid Control to display data from a database in Visual Basic 6 environment. However, it does not allow users to search for and select the information they want to see. In order to search for a certain information, we need to use SQL query. SQL stands for Structures Query Language. Using SQL keywords, we are able to select specific information to be displayed based on certain criteria.

The most basic SQL keyword is SELECT, it is used together with the keyword FROM to select information from one or more tables from a database. The syntax is:

SELECT fieldname1,fieldname2,.....,fieldnameN FROM TableName

fieldname1, fieldname2,......fieldnameN are headings of the columns from a table of a database. You can select any number of fieldname in the query. If you wish to select all the information, you can use the following syntax:

SELECT * FROM TableNam

In order to illustrate the usage of SQL queries, lets create a new database in Microsoft Access with the following filenames ID, Title, Author, Year, ISBN, Publisher, Price and save the table as book and the database as books.mdb in a designated folder.

Next, we will start Visual Basic and insert an ADO control, a DataGrid and three command buttons. Name the three command buttons ascmdAuthor, cmdTitle and cmdAll. Change their captions to Display Author ,Display Book Title and Display All respectively. You can also change the caption of the form to My Books. The design interface is shown below:

Now you need to connect the database to the ADO data control. Please refer to lesson 25 for the details. However, you need to make one change. At the ADODC property pages dialog box, click on the Recordsource tab and select 1-adCmdText under command type and under Command Text(SQL) key in SELECT * FROM book.

Next, click on the command button cmdAuthor and key in the following statements:

Private Sub cmdAuthor_Click()

Adodc1.RecordSource = "SELECT Author FROM book"
Adodc1.Refresh
Adodc1.Caption = Adodc1.RecordSource

End Sub

and for the command button cmdTitle, key in

Private Sub cmdTitle_Click()

Adodc1.RecordSource = "SELECT Title FROM book"
Adodc1.Refresh
Adodc1.Caption = Adodc1.RecordSource

End Sub

Finally for the command button cmdAll, key in

Private Sub cmdAll_Click()

Adodc1.RecordSource = "SELECT * FROM book"
Adodc1.Refresh
Adodc1.Caption = Adodc1.RecordSource

End Sub

Now, run the program and when you click on the Display Author button, only the names of authors will be displayed, as shown below:

and when you click on the Display Book Title button, only the book titles will be displayed, as show below:

Lastly, click on the Display All button and all the information will be displayed.

Lesson 28: More SQL Keywords

In the previous chapter, we have learned to use the basic SQL keywords SELECT and FROM to manipulate database in Visual Basic 6 environment. In this lesson, you will learn to use more SQL keywords. One of the more important SQL keywords is WHERE. This keyword allow the user to search for data that fulfill certain criteria.

The Syntax is as follows:

SELECT fieldname1,fieldname2,.....,fieldnameN FROM TableName WHERE Criteria
The criteria can be specified using operators such as =, >,<, <=, >=, <> and Like.
Using the database books.mdb created in the previous chapter, we will show you a few examples. First of all, start a new project and insert a DataGrid control and an ADO control into the form. . At the ADODC property pages dialog box, click on the Recordsource tab and select 1-adCmdText under command type and under Command Text(SQL) key in SELECT * FROM book.Next, insert one textbox and put it on top of the DataGrid control, this will be the place where the user can enter SQL query text. Insert one command button and change the caption to Query. The design interface is shown below:

Example 28.1: Query based on Author

Run the program and key in the following SQL query statement

SELECT Title, Author FROM book WHERE Author='Liew Voon Kiong'

Where you click on the query button, the DataGrid will display the author name Liew Voon Kiong. as shown below:

Example 28.2:Query based on year

Run the program and key in the following SQL query statement:

SELECT * FROM book WHERE Year>2005

When you click on the query button, the DataGrid will display all the books that were published after the year 2005.

You can also try following queries:

SELECT * FROM book WHERE Price<=80
SELECT * FROM book WHERE Year=2008
SELECT * FROM book WHERE Author<>'Liew Voon Kiong'

You may also search for data that contain certain characters by pattern matching. It involves using the Like operator and the %symbol. For example, if you want to search for a author name that begins with alphabet J, you can use the following query statement

SELECT * FROM book WHERE Author Like 'J%'

Where you click on the query command button, the records where authors' name start with the alphabet J will be displayed, as shown below:

Next, if you wish to rank order the data, either in ascending or descending order, you can use the ORDER By , ASC (for ascending) and DESC(Descending) SQL keywords.

The general formats are

SELECT fieldname1, fieldname2.....FROM table ORDER BY fieldname ASC

SELECT fieldname1, fieldname2.....FROM table ORDER BY fieldname DESC

Example 28.3:

The following query statement will rank the records according to Author in ascending order.

SELECT Title, Author FROM book ORDER BY Author ASC

Example 28.4

The following query statement will rank the records according to price in descending order.

SELECT Title, Price FROM book ORDER BY Price DESC

Lesson 29: Creating Advanced VB database application using ADO control

In previous lessons, you have learned how to design database applications using data control and ADO control. However, those applications are very simple and plain . In this lesson, you will learn how to create a more advanced database application using ADO control. The application you are going to create is known as an electronic library. This electronic library will be able to accept the user registration as well as handling login command that require the user's password, thus enhancing the security aspect of the database. Basically, the application will constitute a welcome menu, a registration menu, a Login menu and the main database menu. The sequence of the menus are illustrated as follow:

2.1 The Welcome Menu

First of all, you need to design the Welcome menu. You can follow the example as follow:

In this form, you need to insert three command buttons and set their properties as follow:

Propery Name	Setting
Form name	frmMainMenu
command button 1 Name	cmdRegister
command button 1 Caption	Register
command button 2 Name	cmdLogin
command button 2 Caption	Login
command button 3 Name	cmdCancel
command button 3 Caption	Cancel

The code is as follows:

Private Sub cmdCancel_Click()
End
End Sub

Private Sub cmdLogin_Click()
Me.Hide
Login_form.Show
End Sub

Private Sub cmdRegister_Click()
Me.Hide
Register.Show

End Sub

*using Me.Hide is a better option then using frmMainMenu.Hide because your program code will be more precise and more readable.

29.2 The Registration Form

If a new user click the Register button, the registration form will appear. An example is illustrated as follow:

This registration forms consist of two text boxes , three command buttons and an ADO control. Their properties are set as follow:

Propery Name	Setting
Form name	frmRegister
textbox 1 name	txtName
textbox 2 name	txtpassword
textbox 2 PasswordChar	*
command button 1 name	cmdConfirm
command button 1 Caption	Confirm
command button 2 name	cmdClear
command button 2 Caption	Clear
command button 3 name	cmdCancel
command button 3 Caption	Cancel
ADO control name	adoUserInfo

note that the PasswordChar of textbox 2 is set as * which means others will not be able to see the actual characters entered by the user, they will only see the * symbol.

The code is as follow:

Private Sub cancel_Click( )
End
End Sub

Private Sub cmdClear_Click( )
txtName.Text = ""
txtpassword.Text = ""

End Sub

Private Sub cmdConfirm_Click()

adoUserInfo.Recordset.AddNew
adoUserInfo.Recordset.Fields("username") = txtName.Text
adoUserInfo.Recordset.Fields("password") = txtpassword.Text
adoUserInfo.Recordset.Update

Me.Hide

Login_form.Show

End Sub

29.3 The Login Menu

The Login menu is illustrated as follow:

There are two text boxes and a command button, their properties are set as follow:

Propery Name	Setting
Textbox 1 name	txtName
Textbox 2 name	txtpassword
Command button 1 name	cmdLogin
Command button 1 Caption	Login
Form name	Login_form

The code is as follow:

Private Sub cmdLogin_Click()

Dim usrname As String
Dim psword As String
Dim usernam As String
Dim pssword As String
Dim Msg As String

Register.UserInfo.Refresh
usrname = txtName.Text
psword = txtpassword.Text

Do Until Register.UserInfo.Recordset.EOF
If Register.UserInfo.Recordset.Fields("username").Value = usrname And Register.UserInfo.Recordset.Fields("password").Value = psword Then
Me.Hide
frmLibrary.Show
Exit Sub

Else
frmRegister.UserInfo.Recordset.MoveNext
End If

Loop

Msg = MsgBox("Invalid password, try again!", vbOKCancel)
If (Msg = 1) Then
Login_form.Show
txtName.Text = ""
txtpassword = ""

Else
End
End If

End Sub
　

29.4 The Main Database Manager

The main database manager is illustrated as follow:

The properties of all controls are listed in the table below:

Propert Name	Setting
Form name	frmLibrary
ADO control name	adoLibrary
ADO visible	False
TextBox 1 name	txtTitleA
TextBox 2 name	txtAuthor
TextBox 3name	txtPublisher
TextBox 4 name	txtYear
TextBox 5 name	txtCategory
Command button 1 name	cmdSave
Command button 1 caption	&Save
Command button 2 name	cmdNew
Command button 2 caption	&New
Command button 3 name	cmdDelete
Command button 3 caption	&Delete
Command button 4 name	cmdCancel
Command button 4 caption	&Cancel
Command button 5 name	cmdNext
Command button 5 caption	N&ext
Command button 6 name	cmdPrevious
Command button 6 caption	&Previous
Command button 7 name	cmdExit
Command button 7 caption	E&xit

The code is as follow:

Private Sub cmdCancel_Click()
txtTitle.Text = ""
txtAuthor.Text = ""
txtPublisher.Text = ""
txtYear.Text = ""
txtCategory.Text = ""
End Sub

Private Sub cmdDelete_Click()
Confirm = MsgBox("Are you sure you want to delete this record?", vbYesNo, "Deletion Confirmation")
If Confirm = vbYes Then
adoLibrary.Recordset.Delete
MsgBox "Record Deleted!", , "Message"
Else
MsgBox "Record Not Deleted!", , "Message"
End If

End Sub

Private Sub cmdExit_Click()
End
End Sub

Private Sub cmdNew_Click()
adoLibrary.Recordset.AddNew

End Sub

Private Sub cmdNext_Click()
If Not adoLibrary.Recordset.EOF Then
adoLibrary.Recordset.MoveNext
If adoLibrary.Recordset.EOF Then
adoLibrary.Recordset.MovePrevious
End If
End If
End Sub

Private Sub cmdPrevious_Click()
If Not adoLibrary.Recordset.BOF Then
adoLibrary.Recordset.MovePrevious
If adoLibrary.Recordset.BOF Then
adoLibrary.Recordset.MoveNext
End If
End If
End Sub

Private Sub cmdSave_Click()

adoLibrary.Recordset.Fields("Title").Value = txtTitle.Text
adoLibrary.Recordset.Fields("Author").Value = txtAuthor.Text
adoLibrary.Recordset.Update

End Sub
　

Lesson 30 : Animation-Part I

Animation is always an interesting and exciting part of programming. Although visual basic is not designed to handle advance animations, you can still create some interesting animated effects if you put in some hard thinking. There are many ways to create animated effects in VB6, but for a start we will focus on some easy methods.

The simplest way to create animation is to set the VISIBLE property of a group of images or pictures or texts and labels to true or false by triggering a set of events such as clicking a button. Let's examine the following example:

This is a program that create the illusion of moving the jet plane in four directions, North, South ,East, West. In order to do this, insert five images of the same picture into the form. Set the visible property of the image in the center to be true while the rest set to false. On start-up, a user will only be able to see the image in the center. Next, insert four command buttons into the form and change the labels to Move North, Move East, Move West and Move South respectively. Double click on the move north button and key in the following procedure:

Sub Command1_click( )

Image1.Visible = False
Image3.Visible = True
Image2.Visible = False
Image4.Visible = False
Image5.Visible = False

End Sub

By clicking on the move north button, only image 3 is displayed. This will give an illusion that the jet plane has moved north. Key in similar procedures by double clicking other command buttons. You can also insert an addition command button and label it as Reset and key in the following codes:

Image1.Visible = True
Image3.Visible = False
Image2.Visible = False
Image4.Visible = False
Image5.Visible = False

Clicking on the reset button will make the image in the center visible again while other images become invisible, this will give the false impression that the jet plane has move back to the original position.

You can also issue the commands using a textbox, the code is shown below:

Private Sub Command1_Click()

If Text1.Text = "n" Then
Image1.Visible = False
Image3.Visible = True
Image2.Visible = False
Image4.Visible = False
Image5.Visible = False

ElseIf Text1.Text = "e" Then
Image1.Visible = False
Image4.Visible = True
Image2.Visible = False
Image3.Visible = False
Image5.Visible = False

ElseIf Text1.Text = "w" Then
Image1.Visible = False
Image3.Visible = False
Image2.Visible = False
Image4.Visible = False
Image5.Visible = True

ElseIf Text1.Text = "s" Then
Image1.Visible = False
Image3.Visible = False
Image2.Visible = True
Image4.Visible = False
Image5.Visible = False
End If

End Sub

Another simple way to simulate animation in VB6 is by using the Left and Top properties of an object. Image.Left give the distance of the image in twips from the left border of the screen, and Image.Top give the distance of the image in twips from the top border of the screen, where 1 twip is equivalent to 1/1440 inch. Using a statement such as Image.Left-100 will move the image 100 twips to the left, Image.Left+100 will move the image 100 twip away from the left(or 100 twips to the right), Image.Top-100 will move the image 100 twips to the top and Image.Top+100 will move the image 100 twips away from the top border (or 100 twips down).Below is a program that can move an object up, down. left, and right every time you click on a relevant command button.

The Code

Private Sub Command1_Click()
Image1.Top = Image1.Top + 100
End Sub

Private Sub Command2_Click()
Image1.Top = Image1.Top - 100
End Sub

Private Sub Command3_Click()
Image1.Left = Image1.Left + 100
End Sub

Private Sub Command4_Click()
Image1.Left = Image1.Left - 100
End Sub

The fourth example let user magnify and diminish an object by changing the height and width properties of an object. It is quite similar to the previous example. The statements Image1.Height = Image1.Height + 100 and Image1.Width = Image1.Width + 100 will increase the height and the width of an object by 100 twips each time a user click on the relevant command button. On the other hand, The statements Image1.Height = Image1.Height - 100 and Image1.Width = Image1.Width -100 will decrease the height and the width of an object by 100 twips each time a user click on the relevant command button

The Code

Private Sub Command1_Click()
Image1.Height = Image1.Height + 100
Image1.Width = Image1.Width + 100
End Sub

Private Sub Command2_Click()

Image1.Height = Image1.Height - 100
Image1.Width = Image1.Width - 100

End Sub

You can try to combine both programs above and make an object move and increases or decreases in size each time a user click a command button.

Lesson 31: Animation - Part II

31.1 Animation using a DragDrop Procedure

Drag and drop is a common windows application where you can drag and drop an object such as a file into a folder or into a recycle bin. This capability can be easily programmed in visual basic. In the following example, I am creating a simulation of dragging the objects into a recycle bin, then drop a fire and burn them away.

In this program, I put 6 images on the form, one of them is a recycle bin, another is a burning recycle bin , one more is the fire, and three more images. In addition, set the property dragmode of all the images( including the fire) that are to be dragged to 1(Automatic) so that dragging is enabled, and set the visible property of burning recycle bin to false at start-up. Besides, label the tag of fire as fire in its properties windows. If you want to have better dragging effects, you need to load an appropriate icon under the dragIcon properties for those images to be dragged, preferably the icon should be the same as the image so that when you drag the image, it is like you are dragging the image along.

The essential event procedure in this program is as follows:
Private Sub Image4_DragDrop(Source As Control, X As Single, Y As Single)

Source.Visible = False
If Source.Tag = "Fire" Then
Image4.Picture = Image5.Picture
End If

End Sub

Source refer to the image to be dragged. Using the code Source.Visible=False means it will disappear after being dragged into the recycle bin(Image4).If the source is Fire, then the recycle bin will changed into a burning recycle bin , which is accomplished by using the code Image4.Picture = Image5.Picture, where Image 5 is the burning recycle bin.

For details of this program, please refer to my game and fun programming page or click this link, Recycle Bin.

31.2 Animation for a complete motion

So far those examples of animation shown in lesson 23 only involve movement of static images. In this lesson, you will be able to create true animation where an action finish in a complete cycle, for example, a butterfly flapping its wings. In the following example, I used eight picture frames of a butterfly which display a butterfly flapping its wing at different stages.

You can actually copy the above images and use them in your program. You need to put all the above images overlapping one another, make image1 visible while all other images invisible at start-up. Next, insert a command button and label it as Animate. Click on the command button and key in the statements that make the images appear and disappear successively by using the properties image.visible=true and image.visible=false. I use If..... Then and Elseif to control the program flow. When you run the program, you should be able to get the following animation.

The Interface

The Code

Private Sub Command1_Click()

If Image1.Visible = True Then
Image1.Visible = False
Image2.Visible = True
ElseIf Image2.Visible = True Then
Image2.Visible = False
Image3.Visible = True
ElseIf Image3.Visible = True Then
Image3.Visible = False
Image4.Visible = True
ElseIf Image4.Visible = True Then
Image4.Visible = False
Image5.Visible = True
ElseIf Image5.Visible = True Then
Image5.Visible = False
Image6.Visible = True
ElseIf Image6.Visible = True Then
Image6.Visible = False
Image7.Visible = True
ElseIf Image7.Visible = True Then
Image7.Visible = False
Image8.Visible = True
ElseIf Image8.Visible = True Then
Image8.Visible = False
Image1.Visible = True
End If

End Sub

If you wish to create the effect of the butterfly flapping its wing and flying at the same time, then you could use the Left and Top properties of an object, such as the one used in the examples of lesson 23. Below is an example of a subroutine where the butterfly will flap its wing and move up at the same time. You can also write subroutines that move the butterfly to the left, to the right and to the bottom.

Sub move_up( )

If Image1.Visible = True Then
Image1.Visible = False
Image2.Visible = True
Image2.Top = Image2.Top - 100

ElseIf Image2.Visible = True Then
Image2.Visible = False
Image3.Visible = True
Image3.Top = Image3.Top - 100

ElseIf Image3.Visible = True Then
Image3.Visible = False
Image4.Visible = True
Image4.Top = Image4.Top - 100
ElseIf Image4.Visible = True Then
Image4.Visible = False
Image5.Visible = True
Image5.Top = Image5.Top - 100
ElseIf Image5.Visible = True Then
Image5.Visible = False
Image6.Visible = True
Image6.Top = Image6.Top - 100

ElseIf Image6.Visible = True Then
Image6.Visible = False
Image7.Visible = True
Image7.Top = Image7.Top - 100

ElseIf Image7.Visible = True Then
Image7.Visible = False
Image8.Visible = True
Image8.Top = Image8.Top - 100
ElseIf Image8.Visible = True Then
Image8.Visible = False
Image1.Visible = True
Image1.Top = Image1.Top - 100
End If

End Sub

Lesson 32: Animation - Part III

32.1 Animation using Timer

All preceding examples of animation that you have learn in lesson 23 and lesson 24 only involve manual animation, which means you need to keep on clicking a certain command button or pressing a key to make an object animate. In order to make it move automatically, you need to use a timer. The first step in creating automatic animation is to drag the timer from the toolbox into the form and set its interval to a certain value other than 0. A value of 1 is 1 milliseconds which means a value of 1000 represents 1 second. The value of the timer interval will determine the speed on an animation.

In the following example, I use a very simple technique to show animation by using the properties Visible=False and Visible=true to show and hide two images alternately. When you click on the program, you should see the following animation.

The Code

Private Sub Timer1_Timer()
If Image1.Visible = True Then
Image1.Visible = False
Image2.Visible = True
ElseIf Image2.Visible = True Then
Image2.Visible = False
Image1.Visible = True
End If
End Sub

Next example shows a complete cycle of a motion such as the butterfly flapping its wing. Previous examples show only manual animation while this example will display an automatic animation once you start the program or by clicking a command button. Similar to the example under lesson 24.2, you need to insert a group of eight images of a butterfly flapping its wings at different stages. Next, insert a timer into the form and set the interval to 10 or any value you like. Remember to make image1 visible while other images invisible at start-up. Finally, insert a command button, rename its caption as Animate and key in the following statements by double clicking on this button. Bear in mind that you should enter the statements for hiding and showing the images under the timer1_timer subroutine otherwise the animation would work. Clicking on the animate button make timer start ticking and the event will run after every interval of 10 milliseconds or whatever interval you have set at design time. In future lesson, I will show you how to adjust the interval at runtime by using a slider bar or a scroll bar. When you run the program, you should see the following animation:

The Code

Private Sub Form_Load()
Image1.Visible = True
x = 0
End Sub

Private Sub Command1_Click()
Timer1.Enabled = True
End Sub

Private Sub Timer1_Timer()
If Image1.Visible = True Then
Image1.Visible = False
Image2.Visible = True

ElseIf Image2.Visible = True Then
Image2.Visible = False
Image3.Visible = True

ElseIf Image3.Visible = True Then
Image3.Visible = False
Image4.Visible = True
ElseIf Image4.Visible = True Then
Image4.Visible = False
Image5.Visible = True
ElseIf Image5.Visible = True Then
Image5.Visible = False
Image6.Visible = True
ElseIf Image6.Visible = True Then
Image6.Visible = False
Image7.Visible = True
ElseIf Image7.Visible = True Then
Image7.Visible = False
Image8.Visible = True
ElseIf Image8.Visible = True Then
Image8.Visible = False
Image1.Visible = True
End If
End Sub

Please refer to my fun and games page for more advanced usage of the above animation , especially the slotmachine.

Lesson 33: Internet and Web Applications Part1:

The Web Browser

If you are bored with existing web browsers, you can create your very own web browser using Visual Basic. In order to create the web browser, launch Visual Basic 6, press Ctrl+T to open up the components window and then select Microsoft Internet Control. The control will appear in the toolbox as a small globe. To insert the Microsoft Internet Control into the form, just drag the globe into the form and a white rectangle will appear in the form. You can resize this control to the size you wish. This control is given the default name WebBrowser1.

To design the interface, you need to insert one combo box which will be used to display the URLs. In addition, you need to insert a few images which will function as command buttons for the user to navigate the Internet; they are the Go command, the Backcommand, the Forward command, the Refresh command and theHome command. You can actually put in the command buttons instead of the images, but using images will definitely improve the look of the browser.

The code for all the commands are relatively easy to write. There are many methods, events, and properties associated with the web browser but you need to know just a few of them to come up with a functional Internet browser

The method navigate is to go the website specified by its Uniform Resource Locator(URL). The syntax is WebBrowser1.Navigate (“URL”). In this program, we want to load the www.vbtutor.net web page at start-up.

The Code

Private Sub Form_Load()

WebBrowser1.Navigate ("http://www.vbtutor.net")

End Sub

In order to show the URL in the combo box and also to display the page title at the form caption after the page is completely downloaded, we use the following statements:

Private Sub

WebBrowser1_DocumentComplete (ByVal pDisp As Object, URL As Variant)

Combo1.Text = URL

Form1.Caption = WebBrowser1.LocationName

Combo1.AddItem URL

End Sub

The following procedure will tell the user to wait while the page is loading.

Private Sub

WebBrowser1_DownloadBegin ()

Combo1.Text = "Page loading, please wait"

End Sub

Lesson 34: Internet and Web Applications Part 2:

The FTP Program

FTP stands for File Transfer Protocol .The File Transfer Protocol is a system for transferring files between two computers connected by the Internet .One of the computers is known as the server and the other one is the client. The FTP program is very useful for website management. The webmaster can update the web pages by uploading the local files to the web server easily , at a much faster speed than the web browser. For normal PC users, the FTP program can also be used to download files from many FTP sites that offer a lot of useful stuffs such as free software, free games, product information, applications, tools, utilities, drivers, fixes and many more things.

The FTP program usually comprises an interface that shows the directories of the local computer and the remote server. Files can be transferred just by clicking the relevant arrows. To log into the FTP site, we have to enter the user name and the password; however, for public domains, we just need to type the word anonymous as the user name and you can leave out the password. The FTP host name takes the form ftp.servername.com, for example, the Microsoft FTP site’s host name is ftp.microsoft.com .If you need to use a FTP program, you can purchase one or you can download a couple of the programs that are available free of charge from the Internet. However, you can also create your very own FTP program with Visual Basic. Visual Basic allows you to build a fully functionally FTP program which may be just as good as the commercial FTP programs.

The engine behind is the Microsoft Internet Transfer Control 6.0 in which you need to insert it into your form before you can create the FTP program. The name of the Microsoft Internet Transfer Control 6.0.is Inet and if you only put in one control, its name will be Inet1.

Inet1 comprises three important properties namely Inet1.URL that is used to identify the FTP hostname,inet1.UserName that is used to accept the username and the Inet1.Password that is used to accept the user’s passwords. The statements for the program to read the hostname of the server, the username and the password entered into Textbox1, Textbox2 and Textbox3 by the user are shown below:

Inet1.URL=Text1.Text

Inet1.UserName=Text2.Text

Inet1.Passoword=Text3.Text

After the user entered the above information, the program will attempt to connect to the server using the following commands, where Execute is the method and DIR is the FTP command that will read the list of files from the specified directory of the remote computer and you need to use the getChunk method to actually retrieve the directory’s information.

Inet1.Execute, "DIR

After connecting to the server, you can choose the file from the remote computer to download by using the statement below:

Inet1.Execute, , "get" & remotefile & localfile

where remotefile is the file of the remote site and localfile is the file of the local system. However, very often you need to provide the full path of the local file, which you can do that by modifying the above syntax to the following syntax:

Inet1.Execute , , "get" & remotefile & localpath & remotefile

The above statements will ensure that the remote file will be downloaded to the location specified by the localpath and the file downloaded will assume the same name as the remote file. For example, if the remote file is readme.txtand the localpath is C:\temp , so the downloaded file will be saved in C:\temp\readme.txt.

In order to monitor the status of the connection, you can use the StateChanged event that is associated with Inet1 together with a set of the state constants that are listed in the following table.

Constant	Value	Description
icHostResolvingHost	1	The control is looking up the IP address of the specified host computer.
icHostResolved	2	The control successfully found the IP address of the specified host computer.
icConnecting	3	The control is connecting to the host computer.
icConnected	4	The control successfully connected to the host computer.
icRequesting	5	The control is sending a request to the host computer.
icRequestSent	6	The control successfully sent the request.
icReceivingResponse	7	The control is receiving a response from the host computer.
icResponseReceived	8	The control successfully received a response from the host computer.
icDisconnecting	9	The control is disconnecting from the host computer.
icDisconnected	10	The control successfully disconnected from the host computer.
icError	11	An error occurred in communicating with the host computer.
icResponseCompleted	12	The request has been completed and all data has been received.

Under the StateChanged event, you use the Select Case…End Select statements to notify the users regarding the various states of the connection. The code is shown below:

Private Sub Inet1_StateChanged(ByVal State As Integer)

Select Case State

Case icError

MsgBox Inet1.ResponseInfo, , "File failed to transfer"

Case icResolvingHost

Label6.Caption = "Resolving Host"

Case icHostResolved

Label6.Caption = "Host Resolved"

Case icConnecting

Label6.Caption = "Connecting Host"

Case icConnected

Label6.Caption = "Host connected"

Case icReceivingResponse

Label6.Caption = "Receiving Response"

Case icResponseReceived

Label6.Caption = "Got Response"

Case icResponseCompleted

Dim data1 As String

Dim data2 As String

MsgBox "Download Completed"

End Select

End Sub

The FTP program that I have created contains a form and a dialog box. The dialog box can be added by clicking on the Project item on the menu bar and then selecting the Add Form item on the drop-down list. You can either choose a normal dialog box or a login dialog box. The function of the dialog box is to accept the FTP address, the username and the password and then to connect to the server. After successful login, the dialog box will be hidden and the main form will be presented for the user to browse the remote directory and to choose certain files to download.

The interface of the login dialog is shown on the right.

The code for the login dialog is,

Option Explicit

Private Sub OKButton_Click()

Inet1.URL = Text1.Text

Inet1.UserName = Text2.Text

Inet1.Password = Text3.Text

Inet1.Execute , "DIR"

Form1.Show

Dialog.Hide

End Sub

Private Sub Inet1_StateChanged(ByVal State As Integer)

Select Case State

Case icError

MsgBox Inet1.ResponseInfo, , "File failed to transfer"

Case icResolvingHost

Label6.Caption = "Resolving Host"

Case icHostResolved

Label6.Caption = "Host Resolved"

Case icConnecting

Label6.Caption = "Connecting Host"

Case icConnected

Label6.Caption = "Host connected"

Case icReceivingResponse

Label6.Caption = "Receiving Response"

Case icResponseReceived

Label6.Caption = "Got Response"

Case icResponseCompleted

Dim data As String

Dim data1 As String

MsgBox "Transfer Completed"

data1 = Inet1.GetChunk(1024, icString)

data = data & data1

Loop While Len(data1) <> 0

Form1.Text6.Text = data

End Select

End Sub

Private Sub CancelButton_Click()

Text1.Text = ""

Text2.Text = ""

Text3.Text = ""

End Sub

retrieve

The statement data1 = Inet1.GetChunk (1024, icString) is to use the getChunk method to grab information of the remote directory and then display the files of the directory in Textbox6.

After logging in, the main form will be presented as shown in the image below:

Lesson 35: Errors Handling in Visual Basic

35.1 Introduction

Error handling is an essential procedure in Visual Basic programming because it can help make the program error-free. An error-free program can run smoothly and efficiently, and the user does not have to face all sorts of problems such as program crash or system hang.

Errors often occur due to incorrect input from the user. For example, the user might make the mistake of attempting to ask the computer to divide a number by zero which will definitely causes system error. Another example is the user might enter a text (string) to a box that is designed to handle only numeric values such as the weight of a person, the computer will not be able to perform arithmetic calculation for text therefore will create an error. These errors are known as synchronous errors.

Therefore a good programmer should be more alert to the parts of program that could trigger errors and should write errors handling code to help the user in managing the errors. Writing errors handling code should be considered a good practice for Visual Basic programmers, so do not try to finish a program fast by omitting the errors handling code. However, there should not be too many errors handling code in the program as it create problems for the programmer to maintain and troubleshoot the program later.

35.2 Writing the Errors Handling Code

We shall now learn how to write errors handling code in Visual Basic. The syntax for errors handling is

On Error GoTo program_label

where program_label is the section of code that is designed by the programmer to handle the error committed by the user. Once an error is detected, the program will jump to the program_label section for error handling.

Example 35.1: Division by Zero

Private Sub CmdCalculate_Click()

Dim firstNum, secondNum As Double
firstNum = Txt_FirstNumber.Text
secondNum = Txt_SecondNumber.Text
On Error GoTo error_handler
Lbl_Answer.Caption = firstNum / secondNum
Exit Sub 'To prevent error handling even the inputs are valid

error_handler:
Lbl_Answer.Caption = "Error"
Lbl_ErrorMsg.Visible = True
Lbl_ErrorMsg.Caption = " You attempt to divide a number by zero!Try again!"

End Sub

Private Sub Txt_FirstNumber_GotFocus()

Lbl_ErrorMsg.Visible = False

End Sub

Private Sub Txt_SecondNumber_GotFocus()

Lbl_ErrorMsg.Visible = False

End Sub

The Output Window

Explanation:

In this example, you design the interface as above. Name the first textbox as Txt_FirstNumber and the second textbox as Txt_SecondNumber. Insert one command button as label it as Calculate. Insert another label and name it as Lbl_Answer to display the answers. If the user enter 0 in the second textbox as shown above, the program will jump to the label error_handler, and the error handling procedure is executed. It will show an error in the Txt_Answer label and an error message in the Lbl_ErrorMsg label.

Notice that Exit sub after the division. It is important because it can prevent the program to execute the error_handler code even though the user does not enter zero in the second textbox.

Lastly, after the error message appeared, the user will click on the textboxes again. When this occur, the error message will disappear both from the answer label and error message label. This is achieved by using the event procedure GotFocus, as shown in the code.

Example 35.2: Nested Error Handling Procedure

By referring to Example 35.1, we need to consider other types of errors made by the user, such as entering non-numeric inputs like letters. Therefore, we need to write error handling code for this error too. It should be put in the first place as soon as the user input something in the textboxes. And the error handler label error_handler1 for this error should be put after the error_handler2label. This means the second error handling procedure is nested within the first error handling procedure. Notice that you have to put an Exit Sub for the second error handling procedure to prevent to execute the first error handling procedure again. The code is as follow:

Private Sub CmdCalculate_Click()

Dim firstNum, secondNum As Double
On Error GoTo error_handler1
firstNum = Txt_FirstNumber.Text
secondNum = Txt_SecondNumber.Text
On Error GoTo error_handler2
Lbl_Answer.Caption = firstNum / secondNum
Exit Sub 'To prevent errror handling even the inputs are valid

error_handler2:
Lbl_Answer.Caption = "Error"
Lbl_ErrorMsg.Visible = True
Lbl_ErrorMsg.Caption = " You attempt to divide a number by zero!Try again!"
Exit Sub
error_handler1:
Lbl_Answer.Caption = "Error"
Lbl_ErrorMsg.Visible = True
Lbl_ErrorMsg.Caption = " You are not entering a number! Try again!"

End Sub

Private Sub Txt_FirstNumber_GotFocus()

Lbl_ErrorMsg.Visible = False

End Sub

Private Sub Txt_SecondNumber_GotFocus()

Lbl_ErrorMsg.Visible = False

End Sub

The Output window

Lesson 36: Compiling and Distributing Your Programs

36.1 Compiling your Visual Basic Program

Once your have completed a VB program, you can compile the program to run as a standalone windows application, without having to launch the Visual Basic IDE. However, before you compile your program, you have to debug your program to make sure it is errors free. Once the program is compiled into an EXE file (executable file), you can not debug it anymore. If you wish to do so, you have to correct the errors and recompile it.

To start compiling your program, click on the menu File and select Make Project1.exe, as show in Figure 36.1. When you click on Make Project1.exe , the Make Project dialog box will appear, as shown in Figure 36.2. In this dialog box, assign a file name to this project and save it in the folder chosen by you. After clicking the OK button, the project properties dialog will appear where you can select the project you wish to compile, as shown in Fgure 36.3. In this example, the project we chose to compile is reversi. The option button in this dialog box let you customize the program you are going to compile. For example, you can enter the title of the program , the program's version and your company name. Clicking on the compile tab will let you decide the kind of code you wish to compile, as shown in Figure 36.4. The default option is native code and it is the best option because it normally runs faster. It requires fewer files to run, particular the VB DLL files. Once you have done that, you can click the OK button to compile the program. Now you program can run as a standalone application. You can start your program without launching the Visual Basic IDE.

Figure 36.1	Figure 36.2
Figure 36.3	Figure 36.4

36.2 Distributing Your Programs

After successfully created a VB program, you might want to market your product, either online or offline. This means that you need to create a package that can be distributed to your potential customers. The package created can be distributed using CD ROM, DVDROM or the Internet. The package will allow the user to install the program to install in the computer with the standard setup routine.

To create the distributable package, you can use the Package and Development Wizard that came with Visual Basic 6. The main purpose of this wizard is to create a setup program that can be used to install the application. Off course, it also does many other jobs like compiling your application and compresses the files for easy distribution.

When you start the Package and Development Wizard, you will be presented with the following dialog box:

First of all, you need to select the project you want to package. Here we have selected the starwar.vbp project. Next, you need to select one of the three options. Here, I suggest you select the first option to let the wizard create the installation package for you to distribute it using CD ROM or the Internet.

Once you click the package option, you will see the following dialog box where you are asked to choose a packaging script:

After clicking the next button, you will see the following dialog box where you will be asked to choose a packaging type. Normally we choose the Standard Setup Package.

The next dialog box that shows up will ask you where to store the package, as shown below:

The next dialog box will show you the files that will be included in the package.

When you click the Finish button, the package will be created and ready for distribution. Here is the packaged files for the starwar program for download at

Setup.exe

SETUP.LST

starwar5.CAB

You must download all the three files into a folder and then run the setup program.

About Me

Thursday 21 August 2014

Lesson1 : Introduction to Visual Basic 6

1.1 The concept of computer programming

Lesson 2: Building Visual Basic Applications

2.1 Creating Your First Application

2.2 Steps in Building a Visual Basic Application

Step 1 : Design the interface by adding controls to the form and set their properties

Step 2 : Write code for the event procedures

Lesson 3-Working With Controls

Lesson 4 : Writing the Code

Private Sub Command1_Click

End Sub

Example 4.2

Example 4.3

Example 4.4

Lesson 5: Managing Visual Basic Data

Lesson 6: Working with Variables

6.1 Assigning Values to Variables

6.2 Using Operators in Visual Basic

Lesson 7 : Controlling Program Flow

7.1 Conditional Operators

7.2 Logical Operators

7.3 Using If.....Then.....Else Statements with Operators

7.4 Nested If... Then...Else Statements

Lesson 8 : Select Case....End select Control Structure

Lesson 9: Looping

9.1 Do Loop

9.3 For....Next Loop

9.4 Nested For...Next Loop

9.5 The While….Wend Loop

Lesson 10: Introduction to VB Built-in Functions

10.1 MsgBox ( ) Function

Lesson 11: Mathematical Functions

Lesson 12: Formatting Functions

Lesson 13: String Manipulation Functions

(i)The Len Function

(vi) The Trim function

(ix) The InStr function

Lesson 14: Creating User-Defined Functions

Lesson 15: Creating VBA Functions For MS Excel

Lesson 16: Arrays

16.1 Introduction to Arrays

16.2 Declaring Arrays

Lesson 17: Working with Files

17.1 Introduction

17.2 Creating a File

Lesson 18: Graphics

Lesson 19: Creating Multimedia Applications-Part I

Lesson 20: Creating Multimedia Applications-Part II

Lesson 21: Creating Multimedia Applications-Part III

Lesson 22: Creating Multimedia Applications-Part IV:

A Multimedia Player

Lesson 23: Creating database applications in VB-Part I

Lesson 24: Creating database applications in VB-Part II

Lesson 25: Creating VB database applications using ADO control

Lesson 26: Using Microsoft DataGrid Control 6.0

Lesson 27: Using SQL queries in Visual Basic 6

Lesson 28: More SQL Keywords

Lesson 29: Creating Advanced VB database application using ADO control

Lesson 30 : Animation-Part I

Lesson 31: Animation - Part II

31.1 Animation using a DragDrop Procedure

31.2 Animation for a complete motion

The Interface

The Code

Lesson 32: Animation - Part III

32.1 Animation using Timer

The Code

Lesson 33: Internet and Web Applications Part1:

The Web Browser

Lesson 34: Internet and Web Applications Part 2:

The FTP Program

Lesson 35: Errors Handling in Visual Basic

Lesson 36: Compiling and Distributing Your Programs

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