创建并添加到会话

Question

I am creating a shopping cart and having some trouble adding the first item to it. The shopping cart code is below:

switch($action) { //decide what to do 

    case "add":

        $_SESSION['cart'][$Item_ID]++; //add one to the quantity of the product with id $product_id 
    break;

    case "remove":
        $_SESSION['cart'][$Item_ID]--; //remove one from the quantity of the product with id $product_id 
        if($_SESSION['cart'][$Item_ID] == 0) unset($_SESSION['cart'][$Item_ID]); //if the quantity is zero, remove it completely (using the 'unset' function) - otherwise is will show zero, then -1, -2 etc when the user keeps removing items. 
    break;

    case "empty":
        unset($_SESSION['cart'][$Item_ID]); //unset the whole cart, i.e. empty the cart. 
    break;

    case "nothing":
    break;
}

When I add an item for the first time (the first one added to the basket) it gives me these errors

Notice: Undefined index: cart in H:\STUDENT\S0190204\GGJ\Basket.php on line 59 Notice: Undefined index: 1 in H:\STUDENT\S0190204\GGJ\Basket.php on line 59

Answer 1

try this

 case "add":
 if(!isset($_SESSION['cart'][$Item_ID])){
  $_SESSION['cart'][$Item_ID]=0;
 }
  $_SESSION['cart'][$Item_ID]++;
  break;

This should work because when you are gonna try to increment first time $_SESSION['cart'][$item_ID] it is not set

see this

$_SESSION['cart'][$Item_ID]++ is equvivalent to

$_SESSION['cart'][$Item_ID] = $_SESSION['cart'][$Item_ID] + 1;

in the above expression $_SESSION['cart'][$Item_ID] is undefined (on right-hand side of assignment)