We've got this little snippet here that in version 3 works properly, however in php4 it has a minor problem. For all $rIA1 values other than 0 it works fine, but when $rIA1==0, empty returns true.

// $rIA1 is between 0 and 4

$rIA1=0;
if (empty($rIA1)) { 
  $filled = 0;
  echo "Please answer question: IA1 <br> ";
}

//Result
Please answer the question: IA1