Add item quantity instead of replacing - php

Question

When i use this add to cart script i erases the already added quantity in session!
But i want it to add the specefied quantity plus the quantity already in basket session.
How to do that?
Scroll to the right on demo (the page i F****d up)//
Live DEMO here http://www.sanwebe.com/assets/php-shopping-cart/index.php
Here is the following code that i use
<?php
session_start();
include_once("config.php");
//empty cart by distroying current session
if(isset($_GET["emptycart"]) && $_GET["emptycart"]==1)
{
$return_url = base64_decode($_GET["return_url"]); //return url
session_destroy();
header('Location:'.$return_url);
}
//add item in shopping cart
if(isset($_POST["type"]) && $_POST["type"]=='add')
{
$product_code = filter_var($_POST["product_code"], FILTER_SANITIZE_STRING); //product code
$product_qty = filter_var($_POST["product_qty"], FILTER_SANITIZE_NUMBER_INT); //product code
$return_url = base64_decode($_POST["return_url"]); //return url
//MySqli query - get details of item from db using product code
$results = $mysqli->query("SELECT product_name,price FROM products WHERE product_code='$product_code' LIMIT 1");
$obj = $results->fetch_object();
if ($results) { //we have the product info
//prepare array for the session variable
$new_product = array(array('name'=>$obj->product_name, 'code'=>$product_code, 'qty'=>$product_qty, 'price'=>$obj->price));
if(isset($_SESSION["products"])) //if we have the session
{
$found = false; //set found item to false
foreach ($_SESSION["products"] as $cart_itm) //loop through session array
{
if($cart_itm["code"] == $product_code){ //the item exist in array
$product[] = array('name'=>$cart_itm["name"], 'code'=>$cart_itm["code"], 'qty'=>$product_qty, 'price'=>$cart_itm["price"]);
$found = true;
}else{
//item doesn't exist in the list, just retrive old info and prepare array for session var
$product[] = array('name'=>$cart_itm["name"], 'code'=>$cart_itm["code"], 'qty'=>$cart_itm["qty"], 'price'=>$cart_itm["price"]);
}
}
if($found == false) //we didn't find item in array
{
//add new user item in array
$_SESSION["products"] = array_merge($product, $new_product);
}else{
//found user item in array list, and increased the quantity
$_SESSION["products"] = $product;
}
}else{
//create a new session var if does not exist
$_SESSION["products"] = $new_product;
}
}
//redirect back to original page
header('Location:'.$return_url);
}
//remove item from shopping cart
if(isset($_GET["removep"]) && isset($_GET["return_url"]) && isset($_SESSION["products"]))
{
$product_code = $_GET["removep"]; //get the product code to remove
$return_url = base64_decode($_GET["return_url"]); //get return url
foreach ($_SESSION["products"] as $cart_itm) //loop through session array var
{
if($cart_itm["code"]!=$product_code){ //item does,t exist in the list
$product[] = array('name'=>$cart_itm["name"], 'code'=>$cart_itm["code"], 'qty'=>$cart_itm["qty"], 'price'=>$cart_itm["price"]);
}
//create a new product list for cart
$_SESSION["products"] = $product;
}
//redirect back to original page
header('Location:'.$return_url);
}
?>

Answer 1

Maybe Change
This:
//found user item in array list, and increased the quantity
$_SESSION["products"] = $product;
To:
//found user item in array list, and increased the quantity
$_SESSION["products"] = $_SESSION["products"] + $product;