php 绝对值

<?php
 $abs = abs(-4.2); // $abs = 4.2; (double/float)
$abs2 = abs(5); // $abs2 = 5; (integer)
$abs3 = abs(-5); // $abs3 = 5; (integer)
?>
<?php
 $flag = 1; // either 0 or 1
$flag = abs($flag - 1);
?>