private void SignUp_User_change(object sender, EventArgs e) //signing up
        {
            User user = new User();

            user.Username = SignUp_User_txt.Text;

            if (Transmitter.CheckUser(user))//check if username  is Available
            {
                SignUp_User_Label.ForeColor = Color.Green;
                SignUp_User_Label.Text      = "OK ✓";
                usercheck = true;
            }
            else
            {
                SignUp_User_Label.ForeColor = Color.Red;
                SignUp_User_Label.Text      = "Username used before";
                usercheck = false;
            }
        }