Programming Perl, 4th Edition

int

int EXPR
int

This function returns the integer portion of EXPR. If you’re a C programmer, you’re apt to forget to use int with division, which is a floating-point operation in Perl:

$average_age = 939/16;      # yields 58.6875 (58 in C)
$average_age = int 939/16;  # yields 58

You should not use this function for generic rounding, because it truncates toward 0 and because machine representations of floating-point numbers can produce counterintuitive results. For example, int(–6.725/0.025) produces –268 rather than the correct –269; that’s because the value is really more like –268.99999999999994315658. Usually, the sprintf, printf, or the POSIX::floor and POSIX::ceil functions will serve you better than will int.

$n = sprintf("%.0f", $f);   # round (not trunc) to nearest integer

To compensate for the inherent bias that always rounding a 5 up would cause, IEEE specifies that rounding be toward the nearest even number on a 5. Therefore, this:

for (–3 ... 3) { printf "%.0f\n", $_ + 0.5 }

Prints the sequence ‒2, ‒2, ‒0, 0, 2, 2, and 4.