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Visual Basic
Looping
Visual Basic allows a procedure to be repeated as many times as long as the processor could support. This is generally called looping .
Visual Basic allows a procedure to be repeated as many times as long as the processor could support. This is generally called looping .
9.1 Do Loop
The format are
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
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. Lets examine the folowing example
9.3 For....Next Loop
The format is:
For counter=startNumber to endNumber (Step increment)
One or more VB statements
Next
Pease refer to example 9.3a,9.3b and 9.3 c
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 9.1
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
Do
num.Text=counter
counter=counter+1
Loop until counter>1000
Example 9.2
Dim sum, n As Integer
Private Sub Form_Activate()
List1.AddItem "n" & vbTab & "sum"
Do
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 find 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.
Example 9.3 a
For counter=1 to 10
display.Text=counter
Next
Example 9.3 b
For counter=1 to 1000 step 10
counter=counter+1
Next
Example 9.3 c
For counter=1000 to 5 step -5
counter=counter-10
Next
*Notice that increment can be negative
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