private void already_registered_user_bttn_Click(object sender, EventArgs e)
        {
            user_alreadyRegistered thisUser = new user_alreadyRegistered();

            thisUser.Show();
            this.Hide();
        }
        private void back_bttn_Click(object sender, EventArgs e)
        {
            this.Close();
            user_alreadyRegistered thisone = new user_alreadyRegistered();

            thisone.Show();
        }