abs()

abs() calculates the absolute value of a number. It is the value itself, when the number is positive or zero, and it is the opposite of the number when the number is negative.

Almost all integers have an absolute value: the only exception is PHP_INT_MIN. Its value is -9223372036854775808, and the actual absolute value would be 9223372036854775808, which is bigger than PHP_INT_MAX.

abs() takes float and int as types. Except for the exception above, giving a float to abs() produces a float, and giving it an integer, produces an integer. Other types are forbidden. Object have to be turned explicitly into a number.

<?php

    $a = -2;
    print abs($a); // 2
    print abs(abs($a)); // 2

?>

Documentation

Related : Floating Point Numbers, integer, Number, Absolute