Visual Basic 2008 Tutorial
Visual Basic 2008 allows a procedure to be repeated as
many times as long as the processor and memorycould support. This is generally called looping . Looping is required when we need to process something repetitively until a certain condition is met. For example, we can design a program that adds a series of numbers until the sum exceeds a certain value, or a program that
asks the user to enter data repeatedly until he/she the word 'Finish'.
In Visual Basic 2008, there are three types of Loops, they are the For.....Next loop, the Do loop. and the While.....End while loop. We shall examine the structure of each of the loops in details as well as demonstrating them with examples.
11.1 For....Next Loop
The format is:
For counter=startNumber to endNumber (Step
One or more VB statements
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.
For its application, you can refer to example 11.1 d.
Example 11.1 a
Dim counter as Integer
For counter=1 to 10
* The program will enter
number 1 to 10 into the list box.
Dim counter , sum As Integer
For counter=1 to 100 step 10
* The program will calculate the
sum of the numbers as follows:
counter, sum As Integer
sum = 1000
For counter = 100 To 5 Step -5
sum - = counter
*Notice that increment can be
negative.The program will compute the
subtraction as follow:1000-100-95-90-..........
Dim n as Integer
For n=1 to 10
If n>6 then
The process will stop when n
greater than 6.
11.2 Do Loop
The formats are
a) Do While condition
one or more VB statements
Block of one
or more VB statements
Loop While condition
c) Do Until condition
Block of one or more VB statements
of one or more VB statements
Loop Until condition
* 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 following example
* The above example will keep on adding until
The above example can be rewritten as
11.3 While ...End While Loop
The structure of a While´.End While is very similar to the Do Loop. it
takes the following format:
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.
Private Sub Button1_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim sum, n As Integer
Dim sum, n As Integer
While n <> 100
n += 1
sum = sum + n
ListBox1.Items.Add(n & vbTab & sum)
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