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Looping Statements
Very often when you write code, you want allow the same block of
code to run a number of times. You can use looping statements in
your code to do this.
In VBScript we have four looping statements:
· Do...Loop statement - loops while or until a condition
is true
· While...Wend statement - use Do...Loop instead
· For...Next statement - run statements a specified number
of times.
· For Each...Next statement - run statements for each item
in a collection or each element of an array
Do...Loop
You can use Do...Loop statements to run a block of code when you
do not know how many repetitions you want. The block of code are
repeated while a condition is true or until a condition becomes
true.
Repeating Code While a Condition is True
You use the While keyword to check a condition in a Do...Loop
statement.
Do While i > 10
some code
Loop
Notice that if i is for example 9, the code inside the loop will
never be executed.
Do
some code
Loop While i > 10
Notice that in this example the code inside this loop will be
executed at least one time, even if i is less than 10.
Repeating Code Until a Condition Becomes True
You use the Until keyword to check a condition in a Do...Loop
statement.
Do Until i = 10
some code
Loop
Notice that if i is equal to 10, the code inside the loop will
never be executed.
Do
some code
Loop Until i = 10
Notice that in this example the code inside this loop will be
executed at least one time, even if i is equal to 10.
Exiting a Do...Loop
You can exit a Do...Loop statement with the Exit Do keyword.
Do Until i = 10
i = i - 1
If i < 10 Then Exit Do
Loop
Notice that the code inside this loop will be executed as long i
is different from 10, and as long as i is greater than 10.
For...Next
You can use For...Next statements to run a block of code when
you know how many repetitions you want.
You can use a counter variable that increases or decreases with
each repetition of the loop, like this:
For i = 1 to 10
some code
Next
The For statement specifies the counter variable i and its start
and end values. The Next statement increases i by 1.
Using the Step keyword, you can increase or decrease the counter
variable by the value you specify.
For i = 2 To 10 Step 2
some code
Next
In the example above, i is increased by 2 each time the loop
repeats. When the loop is finished, total is the sum of 2, 4, 6,
8, and 10.
To decrease the counter variable, you use a negative Step value.
You must specify an end value that is less than the start value.
For i = 10 To 2 Step -2
some code
Next
In the example above, i is decreased by 2 each time the loop
repeats. When the loop is finished, total is the sum of 10, 8,
6, 4, and 2.
Exiting a For...Next
You can exit a For...Next statement with the Exit For keyword.
For Each...Next
A For Each...Next loop repeats a block of code for each item in
a collection, or for each element of an array.
The For Each...Next statement looks almost identical to the
For...Next statement. The difference is that you do not have to
specify the number of items you want to loop through.
dim names(3)
names(0) = "Tove"
names(1) = "Jani"
names(2) = "Hege"
For Each item in names
some code
Next
Examples
1. This example demonstrates how to make a simple
For.....Next loop.
Coding
<html>
<body>
<script language="VBScript">
for i = 0 to 5
document.write("The number is " & i)
document.write("<br>")
next
</script>
</body>
</html>
Output
The number is 0
The number is 1
The number is 2
The number is 3
The number is 4
The number is 5
2. This example demonstrates how you can loop through the 6
headers in html.
Coding
<html>
<body>
<script language="VBScript">
for i = 1 to 6
document.write("<h" & i & ">This is header " & i & "</h" & i &
">")
next
</script>
</body>
</html>
Output
This is header 1
This is header 2
This is header 3
This is header 4
This is header 5
This is header 6
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