ช่วยดู code shopping cart ของผมหน่อยนะครับ มันมีปัญหาตอนคำนวณสินค้า T_T

<?php
				$PID=$_REQUEST[PID];
				
				$_SESSION[sess_id];
				$_SESSION[sess_code];
				$_SESSION[sess_name];
				$_SESSION[sess_price];
				$_SESSION[sess_discount];
				$_SESSION[sess_num];
				if(count($_SESSION[sess_id])=="0"){
					$check=1;
				}elseif(!in_array($PID,$_SESSION[sess_id])){
					$check=1;
				}
				if($check==1){
					$addcart="SELECT * FROM product WHERE p_id='$PID' ";
					$qaddcart=mysql_db_query($dbname,$addcart);
					$rs=mysql_fetch_array($qaddcart);
					
					$_SESSION[sess_id][]=$rs[p_id];
					$_SESSION[sess_code][]=$rs[p_code];
					$_SESSION[sess_name][]=$rs[p_name];
					$_SESSION[sess_discount][]=$rs[p_discount];
					$_SESSION[sess_price][]=$rs[p_price];
					$_SESSION[sess_num][]=1;
				}
				echo"หากหน้าเพจไม่ refresh กรุณา<a href='?p=your_cart'>คลิกที่นี่</a>";
				echo"<meta http-equiv=\"refresh\" content=\"0;URL=?p=your_cart\" />";
			?>

<?php
		
			if(count($id_del)==0){
				$id_del=array();
			}
			for($i=0;$i<count($_SESSION[sess_id]);$i++){
				if(!in_array($_SESSION[sess_id][$i],$id_del)){
					
					$temp_id[]=$_SESSION[sess_id][$i];
					$temp_code[]=$_SESSION[sess_code][$i];
					$temp_name[]=$_SESSION[sess_name][$i];
					$temp_price[]=$_SESSION[sess_price][$i];
					$temp_discount[]=$_SESSION[sess_discount][$i];
					$temp_num[]=$_SESSION[prd_num][$i];		
				}
			}
			$sess_id=$temp_id;
			$sess_code=$temp_code;
			$sess_name=$temp_name;
			$sess_price=$temp_price;
			$sess_discount=$temp_discount;
			$sess_num=$temp_num;
			if($calculate){
				echo"<meta http-equiv=\"refresh\" content=\"0;URL=?p=your_cart\" />";
			}elseif($complete){
				echo"<meta http-equiv=\"refresh\" content=\"0;URL=?p=your_cart_order\" />";
			}elseif($continuebuy){
				echo"<meta http-equiv=\"refresh\" content=\"0;URL=?p=product\" />";
			}
		?>

<?php
				$PID=$_REQUEST[PID];
			
					$addcart="SELECT * FROM product WHERE p_id='$PID' ";
					$qaddcart=mysql_db_query($dbname,$addcart);
					$rs=mysql_fetch_array($qaddcart);
					
					$_SESSION[sess_id][]=$rs[p_id];
					$_SESSION[sess_code][]=$rs[p_code];
					$_SESSION[sess_name][]=$rs[p_name];
					$_SESSION[sess_discount][]=$rs[p_discount];
					$_SESSION[sess_price][]=$rs[p_price];
					$_SESSION[sess_num][]=1;

				echo"หากหน้าเพจไม่ refresh กรุณา<a href='?p=your_cart'>คลิกที่นี่</a>";
				echo"<meta http-equiv=\"refresh\" content=\"0;URL=?p=your_cart\" />";
			?>

<?php
		$complete=$_REQUEST[complete];
		$calculate=$_REQUEST[calculate];
		$continuebuy=$_REQUEST[continuebuy];
		$id_del=$_REQUEST[id_del];
		$prd_num=$_REQUEST[prd_num];
		$ot_id=$_REQUEST[ot_id];
		$hdnLine=$_REQUEST[hdnLine];
		
			for($i=0;$i<count($id_del);$i++){
				if($id_del[$i]!=""){
					$delp="DELETE FROM orders_temp WHERE ot_id='$id_del[$i]' ";
					$qdelp=mysql_db_query($dbname,$delp);
				}
			}
			for($x=0;$x<count($ot_id);$x++){
						$upp="UPDATE orders_temp SET ot_p_qty='$prd_num' WHERE ot_id='$ot_id[$x]' ";
						$qupp=mysql_db_query($dbname,$upp);
			}
			if($calculate){
				echo"<meta http-equiv=\"refresh\" content=\"0;URL=?p=your_cart\" />";
			}elseif($complete){
				echo"<meta http-equiv=\"refresh\" content=\"0;URL=?p=your_cart_order\" />";
			}elseif($continuebuy){
				echo"<meta http-equiv=\"refresh\" content=\"0;URL=?p=product\" />";
			}
		?>

<form action="?p=cal_cart" method="post" name="calculator" id="calculator">
			<table width="100%" border="0" cellspacing="0" cellpadding="0">
              <tr>
                <td width="5%" height="22" align="center" class="table_title"><strong>ลบ</strong></td>
                <td width="46%" class="table_title"><strong>สินค้า</strong></td>
                <td width="15%" align="center" class="table_title"><strong>จำนวน</strong></td>
                <td width="12%" align="left" class="table_title"><strong>ราคา/หน่วย</strong></td>
                <td width="11%" align="left" class="table_title"><strong>ส่วนลด</strong></td>
                <td width="11%" align="left" class="table_title"><strong>รวม</strong></td>
              </tr>
			  <?php
			  	while($fshp=mysql_fetch_array($qshp)){
					$p_id=$fshp[p_id];
					$p_code=$fshp[p_code];
					$p_name=$fshp[p_name];
					$ot_id=$fshp[ot_id];
					$ot_p_qty=$fshp[ot_p_qty];
					$ot_p_price=$fshp[ot_p_price];
					$ot_p_discount=$fshp[ot_p_discount];
					//คำนวณราคาสินค้า
					$total_unit=$ot_p_price*$ot_p_qty;
					$discount=($total_unit*$ot_p_discount)/100;
					$total_unit2=$total_unit-$discount;
					$total=$total+$total_unit2;
			  ?>
              <tr>
                <td align="center" class="quote_title"><input name="id_del[]" type="checkbox" id="id_del[]" value="<?=$ot_id;?>" /></td>
                <td height="22" class="quote_title"><a href="product_detail.php?id=<?=$p_id;?>" target="_blank" title="คลิกเพื่อดูรายละเอียดสินค้า">[<?=$p_code;?>] <?=$p_name;?></a></td>
                <td align="center" class="quote_title"><input name="prd_num[]" type="text" id="prd_num[]" value="<?=$ot_p_qty;?>" size="5" maxlength="3" style="text-align:center">
                  <input name="ot_id" type="hidden" id="ot_id" value="<?=$ot_id;?>" /></td>
                <td align="left" class="quote_title"><? echo number_format($ot_p_price,2);?></td>
                <td align="left" class="quote_title"><? echo number_format($discount,2);?></td>
                <td align="left" class="quote_title"><font color="#0000FF"><? echo number_format($total_unit2,2);?></font></td>
              </tr>
			  <?php
			  } //while
			  ?>
			  <tr>
                <td height="22" colspan="4" align="right" class="table_title"><strong>ราคารวมทั้งหมด</strong></td>
                <td colspan="2" align="center" class="table_title"><strong><font color="#FF0000"><? echo number_format($total,2);?></font> บาท </strong></td>
                </tr>
				<tr>
                <td height="22" colspan="6" align="right"><input name="hdnLine" type="hidden" id="hdnLine" value="<?=$n;?>" />
                <input name="calculate" type="submit" id="calculate" value="คำนวณราคาสินค้า" />
                  <input name="continuebuy" type="submit" id="continuebuy" value="ซื้อสินค้าต่อ" />
                  <input name="complete" type="submit" id="complete" value="ยืนยันสั่งซื้อสินค้า" /></td>
                </tr>
            </table>
			</form>

$complete=$_REQUEST[complete];
		$calculate=$_REQUEST[calculate];
		$continuebuy=$_REQUEST[continuebuy];
		$id_del=$_REQUEST[id_del];
		$prd_num=$_REQUEST[prd_num];
		$ot_id=$_REQUEST[ot_id];
		$hdnLine=$_REQUEST[hdnLine];
		
   echo "เช็คจำนวน ".count($prd_num)."<br>";
  for($i=0; $i<count($prd_num);$i++){
    echo "$i : value ".$prd_num[$i]." id :".$ot_id[$i]."<BR>";
}

$upp="UPDATE orders_temp SET ot_p_qty='$prd_num[$x]' WHERE ot_id='$ot_id[$x]' ";
mysql_query($upp) or die(mysql_error());
echo $upp."<br>";  // ขอดูผลอันนี้หน่อยครับ