programming-examples/php/Basics/PHP program to add the digits of a positive integer repeatedly until the result has a single digit..php

<?php
function add_digits($num)
{
      if ( $num > 0)
      {
      return ($num - 1) % 9 + 1;
      }
      else
      {
          return 0;
      }
}

print_r(add_digits(48)."\n");
print_r(add_digits(59)."\n");
?>