Another procedure that involves decision 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:
9.2 Exiting the Loop
Sometime we need exit to exit a loop prematurely because of a certain condition is fulfilled. The syntax to use is known as Exit Do. You can examine Example 9.2 for its usage.
Do while counter <=1000
* The above example will keep on adding until counter >1000.
The above example can be rewritten as
Loop until counter>1000
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
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 format is:
Please refer to example 9.3a,9.3b and 9.3 c for its usage.
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. Let’s examine example 9.3 d.
Example 9.3 a
For counter=1 to 10
Example 9.3 b
For counter=1 to 1000 step 10
Example 9.3 c
For counter=1000 to 5 step -5
*Notice that increment can be negative
Example 9.3 d
Private Sub Form_Activate( )
9.4 The While….Wend Loop
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