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Tip of the Day
Language: Web
Expertise: Beginner
Aug 19, 2002

The Benefit of Using the For-Next Loop over the While-Wend Loop


We all know that the For-Next and While-Wend loops execute statement(s) as long as the loop condition is true. However, there is a difference between the two. A loop condition is checked each time the While-Wend loop executes/iterates, whereas this is not the case with the For-Next loop (Loop condition is checked only once when this loop executes). Consider the following code:
 
	Dim i,j
	j = 10
	For i = 0 to j
		Response.Write i & "<BR>"
		j = 12
	Next

This loop will execute ten times rather than 12, even though the loop boundary value is changed with each iteration. Now consider the following code:
 
	Dim i,j
	j = 10
	i = 0
	While i <= j
 		Response.Write i & "<BR>"
		j = 12
	Wend

The code is almost the same as the previous code, except that I've used while-wend loop. Notice again that the loop boundary value is changing with each iteration. This will make this loop execute 12 times. The reason is quite evident: in the While-Wend loop, condition is checked with each iteration.

In a nutshell, if you are sure that loop boundary value will never change, then use the For-Next loop. This will greatly enhance the speed of your code. Otherwise, use the While-Wend loop.
Rahim Momin
 
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