The initialization, loop-continuation condition and increment expressions of a for
statement can contain arithmetic expressions. For example, if x = 2
and y = 10
, and x
and y
are not modified in the loop body, the for
header
for ( unsigned int j = x; j <= 4 * x * y; j += y / x )
is equivalent to
for ( unsigned int j = 2; j <= 80; j += 5 )
The “increment” of a for
statement can be negative, in which case it’s really a decrement and the loop actually counts downward (as shown in Section 5.4).
If the loop-continuation condition is initially false, the body of the for
statement is not performed. Instead, execution proceeds with the statement following the for
.
Frequently, the control variable is printed or used in calculations in the body of a for
statement, but this is not required. It’s common to use the control variable for controlling repetition while never mentioning it in the body of the for
statement.
Error-Prevention Tip 5.2
Although the value of the control variable can be changed in the body of a for statement, avoid doing so, because this can lead to subtle logic errors.
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