ในตัวอย่างตะกร้าสินค้า จะทำยังไงให้มัน add qty ได้ทีละหลายๆอันครับ

<table width="517"  border="" bordercolor="#333333">
  <tr>
    <td width="101"bgcolor="#333333"><font color="#FFFFFF">Picture</font></td>
    <td width="101"bgcolor="#333333"><font color="#FFFFFF">ProductID</font></td>
    <td width="82"bgcolor="#333333"><font color="#FFFFFF">ProductName</font></td>
    <td width="79"bgcolor="#333333"><font color="#FFFFFF">Price</font></td>
    <td width="43"bgcolor="#333333"><font color="#FFFFFF">Discount</font></td>
    <td width="36"bgcolor="#333333"><font color="#FFFFFF">Amount</font></td>
    <td width="29"bgcolor="#333333"><font color="#FFFFFF">Cart</font></td>
  </tr>
  <?
  while($objResult = mysql_fetch_array($objQuery))
  {
  ?>
  <tr>
    <td><img src="img/<?=$objResult["Picture"];?>" /></td>
    <td><?=$objResult["ProductID"];?></td>
    <td><?=$objResult["ProductName"];?></td>
    <td><?=$objResult["Price"];?></td>
    <td><?=$objResult["Discount"];?></td>
    <td><input name="qty" type="text" id="qty" size="2" value=1 /></td>
    <td><a href="order.php?ProductID=<?=$objResult["ProductID"];?>">Order</a></td>
  </tr>
  <?
  }
  ?>
</table>

<?
ob_start();
session_start();
	
if(!isset($_SESSION["intLine"]))
{
	 $_SESSION["intLine"] = 0;
	 $_SESSION["strProductID"][0] = $_GET["ProductID"];
	 $_SESSION["strQty"][0] = 1;

	 header("location:show.php");
}
else
{
	
	$key = array_search($_GET["ProductID"], $_SESSION["strProductID"]);
	if((string)$key != "")
	{
		$qtyy =$_POST["qty"][0]; 
		 $_SESSION["strQty"][$key] = $_SESSION["strQty"][$key] + 1;
	}
	else
	{
		
		 $_SESSION["intLine"] = $_SESSION["intLine"] + 1;
		 $intNewLine = $_SESSION["intLine"];
		 $_SESSION["strProductID"][$intNewLine] = $_GET["ProductID"];
		 $_SESSION["strQty"][$intNewLine] = 1;
	}
	
	 header("location:show.php");

}
?>

<?
  $Total = 0;
  $SumTotal = 0;

  for($i=0;$i<=(int)$_SESSION["intLine"];$i++)
  {
	 // echo $_SESSION["qty"][$i];
	  if($_SESSION["strProductID"][$i] != "")
	  {
		$strSQL = "SELECT * FROM product WHERE ProductID = '".$_SESSION["strProductID"][$i]."' ";
		$objQuery = mysql_query($strSQL)  or die(mysql_error());
		$objResult = mysql_fetch_array($objQuery);
		$Total = $_SESSION["strQty"][$i] * $objResult["Price"]*((100-$objResult["Discount"])/100);
		$SumTotal = $SumTotal + $Total;
	  ?>
	  <tr>
		<td><?=$_SESSION["strProductID"][$i];?></td>
		<td><?=$objResult["ProductName"];?></td>
		<td><?=$objResult["Price"];?></td>
		<td><?=$objResult["Discount"];?></td>
		<td><?=$_SESSION["strQty"][$i];?></td>
		<td><?=number_format($Total,2);?></td>
		<td><a href="delete.php?Line=<?=$i;?>">x</a></td>
	  </tr>
	  <?
	  }
  }
  ?>