The do-while Loop
As we saw
earlier, a while
statement allows the
interpreter to execute a block of code repeatedly while a specified
condition remains true
. Due to a
while
loop’s structure, its body will be
skipped entirely if the loop’s condition is not met the first
time it is tested. A do-while
statement lets us
guarantee that a loop body will be executed at least once with
minimal fuss. The body of a do-while
loop
always executes the first time through the loop.
The do-while
statement’s syntax is
somewhat like an inverted while
statement:
do {substatements
} while (condition
);
The keyword do
begins the loop, followed by the
substatements
of the body. On the
interpreter’s first pass through the
do-while
statement,
substatements
are executed before
condition
is ever checked. At the end of
the substatements
block, if
condition
is true
, the
loop is begun anew and substatements
are
executed again. The loop executes repeatedly until
condition
is false
, at
which point the do-while
statement ends. Note
that a semicolon is required following the parentheses that contain
the condition
.
Obviously, do-while
is handy when we want to
perform a task at least once and perhaps subsequent times. In Example 8.2 we duplicate a series of twinkling-star movie
clips from a clip called starParent
and place them
randomly on the Stage. Our galaxy will always contain at least one
star, even if numStars
is set to 0.
Example 8-2. Using a do-while Loop
var numStars = 5;
var i = 1;
do {
// Duplicate the starParent ...
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