Repetition Structures in Visual Basic

A repetition structure allows the programmer to that an action is to be repeated until given condition is true.

Do While... Loop Statement

 

The Do While...Loop is used to execute statements until a certain condition is met. The following Do Loop counts from 1 to 100.
Dim number As Integer
number = 1
Do While number <= 100
number = number + 1
Loop
A variable number is initialized to 1 and then the Do While Loop starts. First, the condition is tested; if condition is True, then the statements are executed. When it gets to the Loop it goes back to the Do and tests condition again. If condition is False on the first pass, the statements are never executed.

While... Wend Statement

A While...Wend statement behaves like the Do While...Loop statement. The following While...Wend counts from 1 to 100
Dim number As Integer

number = 1
While number <=100
number = number + 1
Wend

Do...Loop While Statement

The Do...Loop While statement first executes the statements and then test the condition after each execution. The following program block illustrates the structure:

Dim number As Long
number = 0
Do
number = number + 1
Loop While number < 201

The programs executes the statements between Do and Loop While structure in any case. Then it determines whether the counter is less than 501. If so, the program again executes the statements between Do and Loop While else exits the Loop.

Do Until...Loop Statement

Unlike the Do While...Loop and While...Wend repetition structures, the Do Until... Loop structure tests a condition for falsity. Statements in the body of a Do Until...Loop are executed repeatedly as long as the loop-continuation test evaluates to False.
An example for Do Until...Loop statement. The coding is typed inside the click event of the command button

Dim number As Long
number=0
Do Until number > 1000
number = number + 1
Print number
Loop

Numbers between 1 to 1000 will be displayed on the form as soon as you click on the command button.

The For...Next Loop

The For...Next Loop is another way to make loops in Visual Basic. For...Next repetition structure handles all the details of counter-controlled repetition. The following loop counts the numbers from 1 to 100:

Dim x As Integer
For x = 1 To 50
Print x
Next

In order to count the numbers from 1 yo 50 in steps of 2, the following loop can be used

For x = 1 To 50 Step 2
Print x
Next

The following loop counts numbers as 1, 3, 5, 7..etc

The above coding will display numbers vertically on the form. In order to display numbers horizontally the following method can be used.
For x = 1 To 50
Print x & Space$ (2);
Next
To increase the space between the numbers increase the value inside the brackets after the & Space$.

Following example is a For...Next repetition structure which is with the If condition used.

Dim number As Integer
For number = 1 To 10
If number = 4 Then
Print "This is number 4"
Else
Print number
End If
Next

In the output instead of number 4 you will get the "This is number 4".