FOR-NEXT and DO-WHILE Code Looping

One of the most important concepts in programming with ASP is the idea of ‘looping’. It allows you to perform an action several times without having to write the same code over and over again. Learn how to use FOR-NEXT and DO-WHILE!

The most commonly used looping construct is the FOR-NEXT loop. Very simply, this means that you give the loop a counter, and it will perform the actions within the loop that many times. Say you want to write out 10 lines of code in order to make a book request form. You could actually hand code all 10 lines. But say it was 20 lines, or 100? You see how this becomes inefficient quickly, especially if you later have to make changes.

Instead, you can easily use a loop to do this without a lot of work. You would simply type in:

FOR LoopCtr = 1 to 100
Response.Write "Book #" & LoopCtr & ": _______________________________ <BR>"

This code will go from 1 to 100, and write out
Book #1: ________________________________
Book #2: ________________________________

And so on up to 100. Since you can use that LoopCtr variable to perform calcuations or to write out to the user, this is very, very handy.

The second kind of commonly used loop is the DO-WHILE loop. Instead of the FOR-NEXT, which has a definite beginning and end, DO-WHILE simple continues going until some sort of condition is met. There are all sorts of applications for a DO-WHILE loop. Let’s say you want to take in a name from a user and you want to write every letter of that name on a separate line. You could use a DO-WHILE loop to keep going until you reach the end of the name:

NameString = "Lisa Shea"
DO WHILE len(NameString)> 0
Response.Write left(NameString, 1)<BR>"
NameString = Right(NameString, len(NameString) - 1)

Both sorts of loops are used VERY frequently with database operations, as you loop or move through database rows. Be sure to practice writing loops – they will become extremely important when you move on to more advanced coding!

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