PHP implements factorial operation small code

$sum = 1;
$num = 7;
if( $num>0 ){
for($i=$num;$i>0;$i--){
 $sum*=$i;
 }
 echo $sum;
}elseif( $num<0 ){
//Note here is ++, negative numbers closer to 0 are ++
 for($i=$num; $i<0;$i++){
 $sum*=$i;
 }
 echo $sum;
}else{
 echo "0";
}
?>

PHP