shopping cart, matter with quantity

Question

this is a shoping cart is work kind of fine but the matter is with quantity, when the quantity is 1 i like got the single_price automatically any sugestion:

$global = 0;

if(isset($_POST['update_cart'])){
    if(isset($_POST['qty'.$i])){
        $qty = $_POST['qty'.$i];
    }else{
        $qty+=1;    
    }

    $update_qty = "update cart set qty='$qty'";

    $run_qty = mysqli_query($con, $update_qty); 

    $_SESSION['qty']=$qty;



    $global = $global+ ($single_price*$qty); 


    $total =$total + ($values * $qty);


}

Answer 1

I see a problem with the concat replace this :

$update_qty = "update cart set qty='$qty'";

With this :

$update_qty = "update cart set qty='".$qty."';