Looping Statements Very often when you write code, you want to allow the same block of code to run a number of times. You can use looping...
Looping Statements
Very often when you write code, you want to 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:
- For...Next statement - runs statements a specified number of times.
- For Each...Next statement - runs statements for each item in a collection or each element of an array
- Do...Loop statement - loops while or until a condition is true
- While...Wend statement - Do not use it - use the Do...Loop statement instead
For...Next Loop
You can use a For...Next statement 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 the counter variable (i) by one.
Step Keyword
Using the Step keyword, you can increase or decrease the counter variable by the value you specify.
In the example below, the counter variable (i) is increased by two each time the loop repeats.
For i=2 To 10 Step 2 some code Next |
To decrease the counter variable, you must use a negative Step value. You must specify
an end value that is less than the start value.
In the example below, the counter variable (i) is decreased by two each time the loop repeats.
For i=10 To 2 Step -2 some code Next |
Exit a For...Next
You can exit a For...Next statement with the Exit For keyword.
For Each...Next Loop
A For Each...Next loop repeats a block of code for each item in a collection, or for each element of an array.
dim cars(2) cars(0)="Volvo" cars(1)="Saab" cars(2)="BMW" For Each x in cars document.write(x & "<br />") Next |
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 is 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 |
If i equals 9, the code inside the loop above will never be executed.
Do some code Loop While i>10 |
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 |
If i equals 10, the code inside the loop will never be executed.
Do some code Loop Until i=10 |
The code inside this loop will be executed at least one time, even if i is equal to 10.
Exit 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 |
The code inside this loop will be executed as long as i is different
from 10, and as long as i is greater than 10.
