Java Reference
In-Depth Information
The
progress
is a statement that makes progress toward termination.
Generally, it increments or decrements the loop counter. Note that this statement
does
not
end in a semicolon.
The
repetend
is any statement. Almost always, we write it as a block:
{…}
.
Here is an example that prints the numbers
0..4
:
for
(i= 0; i != 5; i= i + 1) {
System.out.println(i);
}
Semantics of the for-loop
To show how the for-loop is executed, we give equivalent code that uses a
while-loop. First is the
initialization
, then the while-loop. The
conditions
of the
while-loop and for-loop are the same. The repetend of the while-loop consists of
the
repetend
of the for-loop followed by the
progress
part of the for-loop.
initialization
while
(
condition
) {
repetend
progress
}
There is one slight difference between the general for-loop and the general while-
loop when the initialization contains a declaration. The scope of a loop counter
that is declared in the for-loop is only the for-loop; in the while-loop, the scope
extends beyond the while-loop to include any statements that follow it.
Example
Above, we wrote a for-loop that prints the numbers
0..4
. Here is the equiv-
alent while-loop:
i= 0;
while
(i != 5) {
System.out.println(i);
i= i + 1;
}
7.5.3
Developing a for-loop
Developing a for-loop is no different from developing a while-loop. The same
strategy is used for both. In the next development of a for-loop, we illustrate that,
in some cases, progress can be made by decrementing the loop counter.
We develop a loop to print the values
9
,
8
, and so on, down to
2
. As the first
step, we write a postcondition, which we name
R
.
R: 9
,
8
,
…
, down to
2
have been printed
Activity
7-4.3
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