reverse.php

<?php

//reverse string algorithm

function reverse($string) {

  $len = strlen($string);
  $i = 0;

  while($i <= $len) {

    $a = substr($string, -1, 1);
    $string = substr_replace($string, $a, $i, 0);
    $string = substr($string, 0, $len);
    $i++;

  }

  return $string;

}

$string = reverse("mathematics");
print $string;

?>