Update specific value in an array (Shopping Cart)

I am trying to create a shopping cart. I've created the add function, where if productID already exists in the basket, it'll add and extra to the quantity.

And here's my problem:

If you try to add an extra 3 of the same products to an already existing product in the basket - it'll only add 1 more, because I used: $_SESSION['kurv'][$i]['Antal']++;

How do I create it to add the $_POST['iAntal'] to the SESSION?

$iName = $_GET['iName'];
$iId = $_GET['iId'];
$iPrice = $_GET['iPrice'];
$iAntal = $_POST['iAntal'];
$action = $_GET['action'];

     case "add":
        if(isset($_SESSION['kurv']))
                        {
                                $laengde=sizeof($_SESSION['kurv']);
                                for ($i=0; $i<$laengde; $i++)
                                {
                                        if (isset($_SESSION['kurv'][$i]))
                                        {
                                        if ($_SESSION['kurv'][$i]['ProductID'] == $iId)
                                                {
                                                        $fundet=1;
                                                        $_SESSION['kurv'][$i]['Antal']++;
                                                }
                                        }
     开发者_运维技巧                           }
                        }
                        if (!isset($fundet))
                        {
                                $kurv = array(
                                    'ProductID' => $iId,
                                    'Name' => $iName,
                                    'Price' => $iPrice,
                                    'Antal' => $iAntal
                                );
                                $_SESSION['kurv'][] = $kurv;
                        }
    break;

$_SESSION['kurv'][$i]['Antal'] += (int) $_POST['iAntal'];

You can add many products with this:

$quantity = $_GET["quantity"];
$_SESSION['kurv'][$i]['Antal'] = $_SESSION['kurv'][$i]['Antal']+$quantity;