使用递归将数字减少到单个数字

Question

$result = reduce($number);

function reduce($number) {
    $new_number = 0;
    if($number < 10) {
        return $number;
    }           

    $q = floor($number / 10 );
    $r = $number % 10;
    $new_number = $q + $r;

    if($new_number <= 9) {          
        return $new_number;         
    }
    else {
        reduce($new_number);
    }
}

I want to sum the numbers by its digits
For example, if i pass 10, it should return 1+0 = 1
This works if i pass 10
But not working when i pass 100.

Answer 1

You are missing the word return near the end. It should look like this:

return reduce($new_number);