PHP Script for updating Shopping Cart

add.php The backend PHP script

$p_id=$_POST['p_id'];
$qty=$_POST['qty'];

$elements=array("msg"=>"","size_of_cart"=>"0","validation_status"=>"T");

if(!is_numeric($p_id)){$elements['validation_status']="F";
$elements['msg'].="Data Error";}
if(!is_numeric($qty)){$elements['validation_status']="F"; 
$elements['msg'].="Data Error";}

if($elements['validation_status']=='T'){

if(isset($_SESSION['cart']) && !empty($_SESSION['cart'])) {
	//echo " session  is available ";

}else{
	//echo " session is not available ";
	$_SESSION['cart']=array();
}
....
....
}

foreach ($_SESSION['cart'] as $key => $val) {
if($p_id=== $_SESSION['cart'][$key]['p_id']){
	unset($_SESSION['cart'][$key]); // Remove the product
}
}

if($qty !=0){
$b=array("p_id"=>"$p_id","qty"=>$qty);
array_push($_SESSION['cart'],$b); // Items added to cart
$elements['msg'].="Product Added : p_id: $p_id , qty = $qty ";
}else{
$elements['msg'].="Product Removed : p_id: $p_id   ";	
}

$elements['size_of_cart']=sizeof($_SESSION['cart']);

echo json_encode($elements);