Untitled

<?php
include('config.php');
session_start();
global $ID;
$user = $_SESSION['Users'];
$r = $db -> prepare('select * from Users where Username = ?');
$r -> execute(array($user));
$p = $r -> fetchAll(PDO::FETCH_ASSOC);
foreach ($p as $pp){
$ID = $pp['ID'];

}

?>
<html>
<body>
<center>
<form method="post" action="">
    Gebruikersnaam: <input type="text" name="1"><br>
    Wachtwoord: <input type="password" name="2"><br>
    <input type="submit" name="submit" value="Submit">
</form>
</center>
<?php
    if (isset($_POST["submit"])) {
        $one = $_POST["1"];
        $two = $_POST["2"];

        $a = $db->prepare("update Users SET Username=?, Password=? WHERE ID=?");
        $a->execute(array($one, $two, $ID));
        if ($a) {
            echo "<script>alert('Gewijzigd!');</script>";
Header('Location: uitloggen.php');
        } else {
            echo "<script>alert('Helaas, niet gewijzigd!');</script>";
        }
    }
?>
</body>
</html>