使用$ _GET获取输入数据

Question

我在点击添加到购物车按钮时尝试获取产品数量。但每次我这样做，数量总是0。

添加到购物车按钮的代码

function cart(){

if(isset($_GET['add_cart']))
{   
    global $con;
    $ip = getIp();
    $pro_id = $_GET['add_cart'];
    $prod_quan = $_GET['prod_quan'];

    $check_pro = "select * from cart where ip_add = '$ip' AND p_id = '$prod_id" ;

    $run_check = mysqli_query($con, $check_pro);
        if(mysqli_num_rows($run_check)>0){
            echo "";
        }
        else {
            $insert_pro = "insert into cart (orderId,ip_add,qty) values ('$pro_id','$ip','$prod_quan')";
            $run_pro = mysqli_query($con, $insert_pro);

            echo "<script> window.open('index.php','_self')</script>";

        }
}
}//cart()

这里是项目输入字段的代码：

<div id='single_product'>

            <img src='../admin_int/product_images/$prod_img' width='180' height=180'/>
            <h4>Name:</h4><h4> $prod_name</h4>
            <p><b>Price: $ $prod_price</b></p>
            <p><b>Quantity</b><input type='number' name='prod_quan' placeholder='1' min='1' max='9' size='2'/></p>

            <a href='details.php?prod_id=$prod_id' style='float:left; font-size:19px;padding-top:10px;text-decoration:none'>Details</a>

            <a href='index.php?add_cart=$prod_id'><button style = 'float:right; border:1; border-radius:12px; color:blue;
             height:50px; width:50px;
             background-color: #80ff80'>
            Add to Cart</button></a>
        </div>
    ";