ActionScript for Flash MX: The Definitive Guide, Second Edition

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Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

164

Chapter 8

CHAPTER 8

Loop Statements

In Chapter 7, we saw that a conditional causes a statement block to be executed once

if the value of its test expression is

true.Aloop, on the other hand, causes a state-

ment block to be executed repeatedly, for as long as its test expression remains

true.

Loops come in a variety of tasty flavors: while, do-while, for, and for-in. The first

three types have very similar effects, but with varying syntax. The last type of loop,

for-in, is a specialized kind of loop used with objects. We’ll start our exploration of

loops with the while statement, the easiest kind of loop to understand.

The while Loop

Structurally, a while statement is constructed much like an if statement: a main state-

ment encloses a block of substatements that are executed only when a given condi-

tion is

true:

while (condition) {

substatements

}

If condition is true, substatements are executed. But, unlike the if statement, when

the last substatement is finished, execution begins anew at the beginning of the while

statement (that is, the interpreter “loops” back to the beginning of the while state-

ment). The second pass through the while statement works just like the first: the con-

dition is evaluated, and if it is still

true, substatements are executed again. This

process continues