8.2. Loop Terminology
previous section we encountered several new terms. Let's look
at these more formally, so that you'll understand them well
when working with loops:
statement or expression that defines one or more variables used in
the test expression of a loop.
- Test expression
The condition that must be met in order for
the substatements in the loop body to be executed. Often called a
condition or test, or
The statements that modify the variables
used in the test expression before a subsequent test. A typical
update statement increments or decrements the loop's counter.
One complete execution of the test
expression and statements in the loop body. Sometimes referred to as
one loop or one pass.
- Nesting or nested loop
loop that contains another loop so that you can iterate through some
sort of two-dimensional data. For example, you might loop through
each row in a column for all the columns in a table. The outer or
top-level loop would progress through the columns, and the inner loop
would progress through the rows in each column.
- Iterator or index variable
A variable whose value increases or
decreases with each iteration of a loop, usually used to count or
sequence through some data. Loop iterators are often called
counters. Iterators are conventionally named
i, j, and k
or sometimes x, y, and
z. In a series of nested loops,
i is usually the iterator of the top-level loop,
j is the iterator of the first nested loop,
k is the iterator of the second nested loop, and
so on. You can use any variable name you like for clarity. For
example, you can use charNum as the variable name
to remind yourself that it indicates the current character in a
- Loop body
The block of
statements that are executed when a loop's condition is met.
The body may not be executed at all, or it may be executed thousands
- Loop header or loop control
of a loop that contains the loop statement keyword
do-while, or for-in) and
the loop controls. The loop control varies with the type of loop. In
a for loop, the control comprises the
initialization, the test, and the update; in a
while loop, the control comprises simply the
- Infinite loop
loop that repeats forever because its test expression never yields
the value false. Infinite loops cause an error in
ActionScript as discussed later under Section 8.6.3, "Maximum Number of Iterations".
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