function register($link){
    $username = mysqli_real_escape_string($link, $_POST['username']);
    $email = mysqli_real_escape_string($link, $_POST['email']);
    $password = mysqli_real_escape_string($link, $_POST['password']);
    $password2 = mysqli_real_escape_string($link, $_POST['password2']);
    if($password == $password2){
        $password= md5($password);
        $sql = "INSERT INTO users(UserName,email,password)VALUES('$username','$email','$password')";
        mysqli_query($link,$sql);
        $_SESSION['message'] = "You are now registered";
        $_SESSION['username'] = $username;
        header("location: index.php");
    }else{
        $_SESSION['message'] = "Passwords do not match";
    }
}