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VBScript Do While Loop

If you do not know the number of times you need to execute a block of code, then you will be using Do While loops. For example, you want to output the message "Welcome" while the value of the variable x is less than 5. In such case, Do While loop will be used.

<script type="text/vbscript">
Dim x
x=1
Do While x<5
document.write("Welcome.")
x=x+1
Loop
</script>	

If you try executing the code, you will get the output like this:

The block gets executed four times (when x=1,2,3 and 4) and the loop ends when the value of x becomes 5. If you forget the statement x=x+1, then your loop will become a never ending one. This kind of loops is known as infinite loops. Infinite loops could even crash your system. So, while using Do While looping statements, you should make sure that there is some code that will make the looping condition true at one point or another.

If you assign the value 7 to the variable x at the beginning, then the code block will not be executed even once. Suppose you want to execute the block of code at least once regardless of the condition, then you can use Do While loop. Change the code like this:

VBScript Example:

<script type="text/vbscript">
Dim x
x=7
Do 
document.write("Welcome.")
x=x+1
Loop While x<5
</script>

If you execute this code, you will get the message “Welcome” just once. Here the condition is checked only after executing the loop once.

VBScript Do Until Loop

‘Do Until’ loop is also used when you do not know the number of time you need to execute a block of code. The first block of code in Do Until loop (Do While x<5) is equivalent to the given below block of code.

<script type="text/vbscript">
Dim x
x=1
Do Until x=5
document.write("Welcome.")
x=x+1
Loop
</script>

This will give you the same output as the first block of code in Do While loop. You will see the Welcome message four times. Similar to Do .....Loop While, we have Do....Loop Until as well.

If you want to exit a Do While or Do Until loop in between, then you can use Exit Do statement. Suppose you want to exit the block when the value of x becomes 3 in the above program, then you need to code like this:

<script type="text/vbscript">
Dim x
x=1
Do Until x=5
If x=3 Then Exit Do
document.write("Welcome.")
x=x+1
Loop
</script>

If you execute the code, your output will look like this:

Here the loop is exited when the value of x becomes 3.

VBScript While Loop

While....Wend loop is similar to Do While loop though not used commonly. As Do While is more structured than While.....Wend loop, programmers usually use Do While statements.

<script type="text/vbscript">
Dim x
x = 1   
While x < 5   
document.write("Welcome.")
x=x+1
Wend  
</script>	

The output will be

VBScript For-Next Loop

The For-Next loop can be used to execute a block of code for a specific number of times. The “VBScript For loop" specifies the counter variable and its start and end values. The Next statement increases the counter variable by one.

For i = 1 To 5
  document.write("The number is " & i & "")
Next

If you execute the code, you will get the output like this:

VBScript For-Step-Next Loop

By default, the counter variable is incremented by one. If you want to increase or decrease the counter variable by the value you specify, then you can use For....Step....Next loop. Suppose in the above code, you want to increment the counter by 2, then modify your code like this:

For i = 1 To 5 Step 2
  document.write("The number is " & i & "<br />")
Next
</script>

The output of this code will be:

If you want to exit a For Next or For Step Next loop in between, then you can use Exit for statement. Suppose you want to exit the block when the value of i becomes 3 in the above program, then you need to code like this:

<script type="text/vbscript">
For i = 1 To 5 Step 2
  If i=3 Then Exit For
  document.write("The number is " & i & "<br />")
Next
</script>

The output will be:

VBScript For-Each-Next Loop

If you want to repeat a block of code for each item in a collection or for each element of an Vbscript array, then you need to use For....Each....Next loop.

<script type="text/vbscript">
Dim students(4)
students(0)="John"
students(1)="Hanah"
students(2)="Sarah"
students(3)="Kevin"
students(4)="Emma"

For Each x In students
  document.write(x & "<br />")
Next
</script>

The output of the above specified code will be

Code Sample #10

<html>
<head>

<script type="text/vbscript">
Dim name, length
name = InputBox("Enter your name")
length = Len(name)’Gives length of the input string

For i = 1 To length
  txt = Mid(name,i,1)'Returns a specified number of characters from a string, the first parameter is the string, second parameter is the starting position and third parameter is the number of characters to return
  If txt="a" or txt="A" or txt="e" or txt="E" or txt="i" or txt="I" or txt="o" or txt="O" or txt="u" or txt="U" Then 
  counter = counter+1
  End If
Next
document.write("Hi " & name & "!!!Your name contains " & counter & " vowels.")
</script>

</head>
<body>

</body>
</html>