ช่วยดู function genID ให้ผมหน่อยครับว่าทำไม มันทำงานได้แค่ 9 แล้วไม่ยอมทำงานต่อ

<?
function genID($val){
for($i = 0 ; $i < strlen($val) ; $i++){
if(is_numeric($val[$i])) $numberID .= $val[$i];
if(!is_numeric($val[$i])) $nameID .= $val[$i];
}
$sli = strlen($numberID);
for($i = 9-strlen($nameID) ; $i >= 0 ; $i--){
	if($numberID[$i] == 9) $count++;
	if($count != 0){
		$z++;
		$numberID[$sli-$z] = 0;
		$count = 0;
	}
	else $i = 0;
}
$numberID[$sli-$z-1] = $numberID[$sli-$z-1] + 1;
$lastID =  $nameID.$numberID;
return $lastID;
}
?>

<? 
include 'connect.php';
include 'check.php';
$dbquery = mysql_query("select * from product_type order by prot_ID desc limit 1");
$num = mysql_num_rows($dbquery);
if($num != 0){
	$record = mysql_fetch_array($dbquery);
	$protID = genID($record[prot_ID]);
}
else $protID = 'prot000000';
if(!empty($prot_name)){
	$sql = "insert into product_type (prot_ID, prot_name, prot_status) values ('$protID', '$prot_name', '1')";
	$dbquery = mysql_query($sql);
}
?>