phperror

<?php
// including the database connection file

include("config.php");
 session_start();
if($_SESSION){
	if($_SESSION["rank"] == 2){
if(isset($_POST['update']))
{
    $id = $_POST['id'];

    $username=$_POST['username'];
    $email=$_POST['email'];
    $password=$_POST['password'];
	$rank=$_POST['rank'];


    // checking empty fields
    if(empty($username) || empty($email) || empty($password) || empty($rank)) {

        if(empty($username)) {
            echo "<font color='red'>username field is empty.</font><br/>";
        }

        if(empty($email)) {
            echo "<font color='red'>email field is empty.</font><br/>";
        }

        if(empty($password)) {
            echo "<font color='red'>password field is empty.</font><br/>";
        }

		if(empty($rank)) {
            echo "<font color='red'>rank field is empty.</font><br/>";
        }
    } else {
        //updating the table
        $sql = "UPDATE users SET username=:username, email=:email, password=:password, rank=:rank WHERE id=:id";
        $query = $db->prepare($sql);

        $query->bindparam(':id', $id);
        $query->bindparam(':username', $username);
        $query->bindparam(':email', $email);
        $query->bindparam(':password', $password);
		$query->bindparam(':rank', $rank);
        $query->execute();

        // Alternative to above bindparam and execute
        // $query->execute(array(':id' => $id, ':name' => $name, ':email' => $email, ':age' => $age));

        //redirectig to the display page. In our case, it is admin.php
        header("Location: admin.php");
    }
}


//getting id from url
$id = $_POST['id'];

//selecting data associated with this particular id
$sql = "SELECT * FROM users WHERE id=:id";
$query = $db->prepare($sql);
$query->execute(array(':id' => $id));

while($row = $query->fetch(PDO::FETCH_ASSOC))
{
    $username = $row['username'];
    $email = $row['email'];
    $password = $row['password'];
	$rank = $rank['rank'];
}
}
else{
	echo "alleen voor admins beschikbaar.";
}
}
else{
	echo "deze webpagina is niet beschikbaar.";
}
?>
<html>
<head>
    <title>Edit Data</title>
</head>

<body>
    <a href="admin.php">Home</a>
    <br/><br/>

    <form name="form1" method="post" action="edituser.php">
        <table border="0">
            <tr>
                <td>Name</td>
                <td><input type="text" name="username" value="<?php echo $username;?>"></td>
            </tr>
            <tr>
                <td>email</td>
                <td><input type="text" name="email" value="<?php echo $email;?>"></td>
            </tr>
            <tr>
                <td>password</td>
                <td><input type="text" name="password" value="<?php echo $password;?>"></td>
            </tr>
			<tr>
                <td>rank</td>
                <td><input type="text" name="rank" value="<?php echo $rank;?>"></td>
            </tr>
            <tr>
                <td><input type="hidden" name="id" value=<?php echo $_POST['id'];?>></td>
                <td><input type="submit" name="update" value="Update"></td>
            </tr>
        </table>
    </form>
</body>
</html>