ช่วยดูโค๊ดให้หน่อยครับ รวมเงินทั้งหมดในรายการสั่งซื้อ เป็นราคารวมอีกทีครับ

<? 
$n=0;
$total_cost=0;   // new line
$cmd_st= "select * from saletemp where sale_id = '$row_s[sale_id]'";
$result_st = mysql_query($cmd_st,$link);
while($row_st=mysql_fetch_array($result_st)){
	$cmd_pros = "select * from productstock where pros_id = '$row_st[pros_id]'"; 
	$result_pros = mysql_query($cmd_pros,$link); 
	$row_pros = mysql_fetch_array($result_pros);
	$cmd_num = "select * from saletemp where pro_auto = '$row_pros[pro_auto]' and sale_id='$row_s[sale_id]' "; 
	$result_num = mysql_query($cmd_num,$link); 
	$num = mysql_num_rows($result_num);
	$cmd_pro = "select * from product where pro_auto = '$row_pros[pro_auto]'"; 
	$result_pro = mysql_query($cmd_pro,$link); 
	$row_pro = mysql_fetch_array($result_pro);
	if($test != $row_st[pro_auto]){
		$n++;
		$cost=$row_pro[pro_pricesale]*$num;
                $total_cost+=$cost;
		if($row_s[sale_due] == $fullday) {
			echo"<b><font size='2' color = 'blue'>$n : $row_pro[pro_name] <font size='1' color = 'green'>[ $num ชิ้น $cost bath ]</font><BR>";
		}
		else {
			echo"<font size='2'>&nbsp;&nbsp;$n : $row_pro[pro_name] <font size='1' color = 'green'>[ $num ชิ้น $cost bath ]</font><BR>";
		}
	}
	$test = $row_st[pro_auto];
}
?>	
</td>
<td align="center" bgcolor="#CCCCCC">
<?	
if($row_s[sale_due] == $fullday) {
	echo"<b><font size='2' color = 'blue'>$total_cost</font></b>"; 
}
else {
	echo"<font size='2'>$total_cost";
}
?>	 
</td>