php: converting number to alphabet and vice versa

Question

So I have this function:

function toAlpha($data){
    $alphabet =   array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z');
    $alpha_flip = array_flip($alphabet);
    if($data <= 25){
      return $alphabet[$data];
    }
    elseif($data > 25){
      $dividend = ($data + 1);
      $alpha = '';
      $modulo;
      while ($dividend > 0){
        $modulo = ($dividend - 1) % 26;
        $alpha = $alphabet[$modulo] . $alpha;
        $dividend = floor((($dividend - $modulo) / 26));
      } 
      return $alpha;
    }
}

which given a number converts it into character and it works fine

but then I also want a reverse function of this that given any output of this function, return the exact input that was put in to produce that output and I tried this:

function toNum($data){
$alphabet =   array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z');
    $alpha_flip = array_flip($alphabet);
  if(strlen($data) == 1){
          return (isset($alpha_flip[$data]) ? $alpha_flip[$data] : FALSE);
        }
        else if(strlen($data) > 1){
          $num = 1;
          for($i = 0; $i < strlen($data); $i++){
            if(($i + 1) < strlen($data)){
              $num *= (26 * ($alpha_flip[$data[$i]] + 1));
            }
            else{
              $num += ($alpha_flip[$data[$i]] + 1);
            }
          }
          return ($num + 25);
        }
}

but it's not working properly...toAlpha(728) is producing 'aba' but toNum('aba') is producing 1378 rather than 728...

what did I do wrong? how can I fix the reverse function so that it works properly?

thanks in advance!

Answer 1

Shortest way, in PHP >= 4.1.0

$alphabet = range('A', 'Z');

echo $alphabet[3]; // returns D

echo array_search('D', $alphabet); // returns 3