Visual Basic 2008 Tutorial

Lesson 12: Functions-Part I

 

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A function is similar to a normal procedure but the main purpose of the function is to accept a certain input 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 syntax of a function is
              FunctionName (arguments)

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

In this lesson, we are going to learn two very basic but useful internal functions of Visual basic , i.e.  the MsgBox( ) and InputBox ( ) functions.

   

12.1 MsgBox ( ) Function

The objective of MsgBox is to produce a pop-up message box and 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 ton Table 12.1 for types of command button displayed. The Title argument will display the title of the message board.

Table 12.1: 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 constants in place of integers for the second argument to make the programs more readable. In fact, VB6 will automatically shows up a list of named constants  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 12.2 shows the values, the corresponding named constant and buttons.

Table 12.2 : 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 12.1

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim testmsg As Integer
testmsg = MsgBox("Click to test", 1, "Test message")
If testmsg = 1 Then
MessageBox.Show("You have clicked the OK button")
Else
MessageBox.Show("You have clicked the Cancel button")
End If
End Sub

To make the message box looks more sophisticated, you can add an icon besides the message. There are four types of icons available in VB2008 as shown in  Table 12.3

Value
Named Constant

Icon 

16
vbCritical
32
vbQuestion
48
vbExclamation
64
vbInformation

Example 12.2

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim testMsg As Integer
testMsg = MsgBox("Click to Test", vbYesNoCancel + vbExclamation, "Test Message")

If testMsg = 6 Then
MessageBox.Show("You have clicked the yes button")
ElseIf testMsg = 7 Then
MessageBox.Show("You have clicked the NO button")
Else
MessageBox.Show("You have clicked the Cancel button")
End If

End Sub 

The first argument, Prompt, will display the message. The output is as shown below:


 

 

 

12.2 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. In VB2005, you can use the following format:

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 enter.
  • x-position and y-position - the position or tthe coordinates of the input box.

However, the format won't work in VB2008 because InputBox is considered a namespace. So, you need to key in the full reference to the Inputbox namespace, which is

Microsoft.VisualBasic.InputBox(Prompt, Title, default_text, x-position, y-position)

The parameters remain the same.

Example 12.3

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim userMsg As String


userMsg = Microsoft.VisualBasic.InputBox("What is your message?", "Message Entry Form", "Enter your messge here", 500, 700)

If userMsg <> "" Then
MessageBox.Show(userMsg)
Else
MessageBox.Show("No Message")
End If
End Sub

The inputbox will appear as shown in the figure below when you press the command button

 

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