<?php
class Solution
{
    public function addDigits($num) 
    {
        while ($num > 10)
        {
            $tmp = 0;<br />
            while ($num &gt; 0)
            {
                $tmp += $num % 10;
                $num = intval($num / 10);<br />
            }
            $num = $tmp;
        }
        return $num;
    }
}
$solution = new Solution();
echo $solution-&gt;addDigits(381);
?&gt;