php session error - session

Question

I was trying to make a shopping cart and got a code from web..
<?php
session_start();
require_once 'class/Item.php';
$product_id = $_REQUEST['i_id'];
$action = $_REQUEST['action'];
$item= new Item();
if($product_id && !$item->productExists($product_id)) {
die("Error. Product Doesn't Exist");
}
switch($action) {
case "add":
$_SESSION['cart'][$product_id]++;
break;
case "remove":
$_SESSION['cart'][$product_id]--;
if($_SESSION['cart'][$product_id] == 0) unset($_SESSION['cart'][$product_id]);
break;
case "empty":
unset($_SESSION['cart']);
break;
}
?>
but durring adding the first item to the cart it goes error. How can I correct it.
Error:
Notice: Undefined index: cart in C:\wamp\www\website\store_esp\addtocart.php on line 16
Notice: Undefined index: 2 in C:\wamp\www\website\store_esp\addtocart.php on line 16

Answer 1

Looks like you may be trying to manipulate variables that aren't setup yet. Make sure you're checking that $_SESSION['cart'][$product_id] exists before you do something on it:
if(!isset($_SESSION['cart'][$product_id]))
$_SESSION['cart'][$product_id] = 0;
switch($action) {
...

Answer 2

Try changing this:
$_SESSION['cart'][$product_id]++;
to this:
if (isset($_SESSION['cart'][$product_id])) {
++$_SESSION['cart'][$product_id];
} else {
$_SESSION['cart'][$product_id] = 1;
}

Answer 3

Without knowing the error, it's impossible to tell for sure. But using my deductive powers, I think the problem is here:
$_SESSION['cart'][$product_id]++;
It should be this:
if (isset($_SESSION['cart'][$product_id])) {
$_SESSION['cart'][$product_id]++;
} else {
$_SESSION['cart'][$product_id] = 1;
}
And you need to change this:
session_start();
// add this part
if (!isset($_SESSION['cart'])) {
$_SESSION['cart'] = array();
}
require_once 'class/Item.php';
$product_id = $_REQUEST['i_id'];
$action = $_REQUEST['action'];