Visual Basic (2008 Express)
Constructs

In VB the instructions are executed in the order they are written, but there are exceptions...

 
Selection : The syntax for this is...

 

If (boolean expression) Then 
    statement 1
    statement 2
    statement 3
Else
    statement 4
    statement 5
End if

 

A boolean expression is a statement that can either be TRUE or FALSE.
Eg. (Name="Tom")
or
(Mark > 50)
The  statements 1, 2 and 3 will only be executed if the boolean expression is TRUE. If it is FALSE, then statements 4 and 5 will be executed.

The Else section may be left out.

 
Example : An exam mark is input. If the mark is 50 or more then the message "PASS" is output. Otherwise the message "FAIL" is output.
Dim ExamMark As Integer

ExamMark = InputBox("Please enter the mark")

If (ExamMark >= 50) Then
    MsgBox("Pass")
Else
    MsgBox("Fail")
End If

 
 
 
Repetition 

If the number of times a loop is to be executed is known use a For...Next Loop.

Example : Add each of 10 Marks stored in an array to a ListBox...

 
Dim Mark(9) As Integer

Mark(0) = 65
Mark(1) = 48
Mark(2) = 78
Mark(3) = 60
Mark(4) = 39
Mark(5) = 71
Mark(6) = 93
Mark(7) = 55
Mark(8) = 62
Mark(9) = 51

Dim i As Integer

For i = 0 To 9
    ListBox1.Items.Add(Mark(i))
Next

 

The resulting ListBox is shown here.
Loops that are repeated until a condition is met are programmed using either...

Do...Loop Until (condition)

or

Do While (condition)...Loop

 

 The condition is a boolean expression, that is either TRUE or FALSE.
Example : A sequence of exam marks is to be input, until the number 0 is input.

 
Do

    Mark = InputBox("Please enter mark")

Loop Until (Mark = 0)

 

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