PHP：如何在url中传递get值

Question

I want to pass both stock (user input) and id in one url one I try this I get Undefined index: stock
is the way I'm passing the input value wrong ?

<?php



session_start();
$sql1 = "SELECT * FROM tbl_customers WHERE customers_id='1'";

$sql = "SELECT * FROM tbl_products";

$get = mysqli_query($conn, $sql1) or die(mysqli_error($conn));
$row = mysqli_fetch_array($get);

$customerName = $row['customer_email'];
echo "Welcome $customerName";



$data= mysqli_query($conn, $sql) or die(mysqli_error($conn));


while ($row = mysqli_fetch_assoc($data)) {
    $pid = $row['pid'];
    echo "<form action='' method='GET'>

 <input type=text name=stock value=1><br>
<a href='stock.php?id=" . $pid . "?stock=" . $_GET['stock'] . "'> Add</a>

                      </form>";




}

?>

thank you everyone for your help this is what I did to fix the error my get value is always empty If I don't press enter

echo "<form action='' method='GET'>

                     <input type=text name=stock value=1><br>

                             </form>";
    $_GET['stock'] = 1;
    if (isset($_GET["stock"])) {
        $x = $_GET['stock'];
        echo "<a href='stock.php?id=" . $pid . "&stock=" . $_GET['stock'] . "'> Add</a>";
    }

Answer 1

Just change ? with & before stock.

  echo "<form action='' method='GET'><input type=text name=stock value=1><br>
<a href='stock.php?id=" . $pid . "&stock=" . $_GET['stock'] . "'> Add</a> </form>";