The for Loop
A for
loop is essentially synonymous with a
while
loop but is written with more compact
syntax. Most notably, the loop header can contain both initialization
and update statements in addition to the test expression.
Here’s the syntax of the for
loop:
for (initialization
;condition
;update
) { substatements }
The for
loop places the key components of a loop
tidily in the loop header, separated by semicolons. Before the first
iteration of a for
loop, the
initialization
statement is performed
(once and only once). It is typically used to set the initial value
of an iterator variable. As with other loops, if
condition
is true
,
substatements
are executed. Otherwise, the
loop ends. At the end of each loop iteration,
the update
statement is executed, 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 constructed 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 scanning 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 may optionally use more than one iterator variable. A
while
loop with multiple iterators may look like
this:
var i = 1; var j = 10; while (i <= ...
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