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".
