3v4l.org

run code in 300+ PHP versions simultaneously
<?php $dni = '342501198701065'; $row = str_split(strrev($dni)); $letters = array_combine(range(0,25), range('a', 'z')); //now just use: foreach($row as $n){ $dni_a[] = $letters[$n]; } $dni2 = implode($dni_a); echo $dni2;

preferences:
57.53 ms | 402 KiB | 5 Q