- substr: documentation ( source)
- array_slice: documentation ( source)
<?php
function sum($arr) {
if ( empty($arr) ) {
return;
}
return $arr[0] + sum(array_slice($arr, 1));
}
function rev($str) {
if ( ! $str ) {
return;
}
return rev(substr($str,1)) . $str{0};
}
echo sum(array(1,2,3,4,5));
echo rev('hola mundo');