ActionScript for Flash MX: The Definitive Guide, Second Edition

This is the Title of the Book, eMatter Edition

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

170

|

Chapter 8: Loop Statements

one or more iterator variables. As with other loops, if condition is true,

substatements are executed. Otherwise, the loop ends. Even though it appears in the

loop header, the

update statement is executed at the end of each loop iteration,

before

condition is tested again to see if the loop should continue. Here’s a typical

for loop that simply counts from 1 to 10:

for (var i = 1; i <= 10; i++) {

trace("Now serving number " + i);

}

It’s easier to understand how a for loop works when you see its equivalent con-

structed using the while loop syntax:

var i = 1;

while (i <= 10) {

trace("Now serving number " + i);

i++;

}

Once you’re used to the for syntax, you’ll find it saves space and allows for easy

interpretation of the loop’s body and controls.

Multiple Iterators in for Loops

If we want to control more than one factor in a loop, we can use more than one itera-

tor variable. A while loop with multiple iterators might look like this:

var i = 1;

var j = 10;

while (i <= 10) {

trace("Going up " + i);

trace("Going down " + j);

i++;

j--;

}

The same effect can be achieved in a for statement using the comma operator:

for (var i = 1, j = 10; i <= 10; i++, j--) {

trace("Going up " + i);

trace("Going down " + j);

}

Notice that the var keyword is listed only once—it applies to ...