Undefined variable

[Altec]

I've set up a development server so I don't have to mess around with FTP. I've decided to develop with error_reporting to E_ALL so I can see everything PHP whines about. In this case I'm getting an undefined variable error for $output in this class:

<?php
/* @author Matej Koval 
  * http://www.codegravity.com/projects/mathguard
  *
  * Edited by Steven, author of PYGuestbook, for smaller code size and speed improvements
  * htmlpro@gmail.com, http://www.phreakyourgeek.com/
*/
class mathGuard {
     function produceOutput($prime) {
         $a = rand() % 10; $b = rand() % 10;
         $code = mathGuard::generateCode($a,$b,$prime);
         $output = '<table><tr><td><pre style="font-size:5px; font-weight: bold; color:red; padding:0px; margin: 0px; line-height:4px;">'."\n\n".MathGuard::renderExpression($a,$b).'</pre></td><td><input type="text" name="mathguard_answer" size="2" maxlength="2"/></td></tr></table><input type="hidden" name="mathguard_code" value="'.$code.'" />';
         return $output;
     } function decToBin($dec) {
         $pattern = '123456789ABCDEFGHIJKLMNOPQRTSTUWXYZ'; $output = '   '; $i = 0;
         do {
             if($dec % 2) { $rand = rand() % 34; $output { 2 - $i } = $pattern { $rand }; }
             else { $output { 2 - $i } = ' '; }
             $dec = (int) ($dec / 2); $i++;
         } while($dec > 0); return $output;
     } function renderExpression($a,$b) {
         $number = array(
             array(7,5,5,5,7), array(2,6,2,2,7),
             array(7,1,7,4,7), array(7,1,7,1,7),
             array(4,5,7,1,1), array(7,4,7,1,7),
             array(7,4,7,5,7), array(7,1,1,1,1),
             array(7,5,7,5,7), array(7,5,7,1,7)
         ); $plus = array(0,2,7,2,0); $eq = array(0,7,0,7,0);
         for($line = 0; $line < 5; $line++) {
             /*start*/$output .= mathGuard::decToBin($number[$a][$line]).'   '.mathGuard::decToBin($plus[$line]).'   '.mathGuard::decToBin($number[$b][$line]).'   '.mathGuard::decToBin($eq[$line])."\n";
             $output = str_replace('0',' ',$output);
         } return $output;
     } function encode($input,$prime) { return md5($input.date("H").$prime); }
     function generateCode($a,$b,$prime) { $code = mathGuard::encode($a + $b,$prime); return $code; }
     function checkResult($mathguard_answer,$mathguard_code,$prime = 37) {
         $result_encoded = mathGuard::encode($mathguard_answer,$prime); if($result_encoded == $mathguard_code) { return true; } else { return false; }
     } function insertQuestion($prime = 37) { $output = mathGuard::produceOutput($prime); return $output; }
     function returnQuestion($prime = 37) { $output = mathGuard::produceOutput($prime); return $output; }
}
?>

The line is marked with /*start*/. How can I fix this? I tried defining it as a private varibale with it's value to null, but that didn't work.

[sasa]

declare variable at start of function

$output = '';