if($_SERVER["REQUEST_METHOD"] == "POST") {
  // username and password sent from form
$username = mysqli_real_escape_string($link, $_POST['username']);
$password = mysqli_real_escape_string($link, $_POST['password']);

$result = mysqli_query($link, "SELECT * FROM users WHERE username LIKE '$username' AND password LIKE '$password'");

if($result === FALSE) {
    die(mysql_error()); // TODO: better error handling
}

while($row = mysqli_fetch_array($result))
{

echo $row['username'];
}

  echo var_dump($result);
  $active = $row['active'];

  $count = mysqli_num_rows($result);

  // If result matched $username and $password, table row must be 1 row

  if($count == 1) {

     $_SESSION['login_user'] = $username;

       // check the user_type
     if($row["user_type"] == "teacher")
     {
        header("Location: teacher.php")
     }
     elseif($row["user_type"] == "parent")
     {
        header("Location: parent.php")
     }
     elseif($row ["user_type"] == "student")
     {
        header("Location: student.php")
     }
    elseif($row ["user_type" == "HOD")
    {
        header("Location: HOD.php")
    }
    else {
        echo "no account type!";

  }else {
     $error = "Your Login Name or Password is invalid";
  }
}
?>