php generates column numbers in excel

/**
* Use php code to generate serial numbers in excel or csv files
*/
public function loop(){
  $loop = 0;
  $charnum = 65;
  for(; $loop < 150; $loop++){
   $quotient = intval($loop / 26);
   $remainder = $loop % 26;
   $f = $quotient>0? chr($charnum+$quotient-1) : '';
   $s = $remainder>=0? chr($charnum+$remainder) : '';
   echo $loop .' | '. $quotient .' | '. $remainder .' | '. $f . $s ."";
  } // bbs.it-home.org
 }