// It registers the new user as long as all controls hold text
        private void buttonRegister_Click(object sender, EventArgs e)
        {
            //variables to be used
            string username = "", password = "", password2 = "", firstname = "", lastname = "", email = "", clientType = "", userType = "";
            Int32  phone = 0;

            //It checks that the text and combo boxes have something typed in them
            bool hasText = checkTextControls();

            if (!hasText)
            {
                MessageBox.Show("Please make sure all fields have data.");
                comboBoxUserType.Focus();
                return;
            }

            //It checks that the username doesn't exist yet in the DB
            bool userOK = checkUsername(textBoxUserName.Text.Trim(), comboBoxUserType.Text);

            if (!userOK)
            {
                MessageBox.Show("This user already exists in the Data Base, please try another one.");
                textBoxUserName.BackColor = Color.LightCoral;
                textBoxUserName.Focus();
                return;
            }
            //It checks that the password==password2
            bool passOK = checkPassword(textBoxPassword.Text.Trim(), textBoxPassword2.Text.Trim());

            if (!passOK)
            {
                MessageBox.Show("Please make sure the password in both password fields is the same.");
                textBoxPassword.BackColor  = Color.LightCoral;
                textBoxPassword2.BackColor = Color.LightCoral;
                textBoxPassword.Focus();
                return;
            }
            //It checks that the email is a proper one
            bool emailOK = checkEmail(textBoxEmail.Text.Trim());

            if (!emailOK)
            {
                MessageBox.Show("Please insert a proper email in the field.");
                textBoxEmail.BackColor = Color.LightCoral;
                textBoxEmail.Focus();
                return;
            }
            //It checks that the phone number introduced is numbers if the control is enabled
            if (textBoxPhone.Enabled == true)
            {
                bool phoneOK = int.TryParse(textBoxPhone.Text.Trim(), out phone);
                if (!phoneOK)
                {
                    MessageBox.Show("You can only write numbers in the phone field.");
                    textBoxPhone.BackColor = Color.LightCoral;
                    textBoxPhone.Focus();
                    return;
                }
            }

            //(1) GET the data from the textboxes and store into variables created above, good to put in a try catch with error message
            try
            {
                userType  = comboBoxUserType.Text;
                username  = textBoxUserName.Text.Trim();
                password  = textBoxPassword.Text.Trim();
                password2 = textBoxPassword2.Text.Trim();
                firstname = textBoxFirst.Text.Trim();
                lastname  = textBoxLast.Text.Trim();
                email     = textBoxEmail.Text.Trim();
                switch (userType)
                {
                case "Admins":
                    break;

                case "Clients":
                    phone      = int.Parse(textBoxPhone.Text.Trim());
                    clientType = comboBoxClientType.Text.Trim();
                    break;

                case "Instructors":
                    phone = int.Parse(textBoxPhone.Text.Trim());
                    break;

                default:
                    break;
                }
            }
            catch
            {
                //Error message, more useful when you are storing numbers etc. into the database.
                MessageBox.Show("Please make sure your data is in correct format.");
                return;
            }

            //(2) Execute the INSERT statement, making sure all quotes and commas are in the correct places.
            try
            {
                var insertClientQuery = "";
                //It sends a different insert statement depending on the User Type Selection
                switch (userType)
                {
                case "Admins":
                    insertClientQuery = $"INSERT INTO {userType} VALUES('{username}', '{password}', '{firstname}', '{lastname}', '{email}')";
                    break;

                case "Clients":
                    insertClientQuery = $"INSERT INTO {userType} VALUES('{username}', '{password}', '{firstname}', '{lastname}', '{email}', {phone}, '{clientType}')";
                    break;

                case "Instructors":
                    insertClientQuery = $"INSERT INTO {userType} VALUES('{username}', '{password}', '{firstname}', '{lastname}', '{email}', {phone})";
                    break;

                default:
                    break;
                }
                SQL.executeQuery(insertClientQuery);
            }
            catch (Exception)
            {
                MessageBox.Show("Register attempt unsuccessful.  Check insert statement.  Could be a Username conflict too.");
                return;
            }



            //success message for the user to know it worked
            MessageBox.Show("Successfully Registered as " + userType + ": " + firstname + " " + lastname + ". Your username is: " + username);

            //Go back to the login page since we registered successfully to let the user log in
            Hide();                                 //hides the register form
            LoginPage login = new LoginPage();      //creates the login page as an object

            login.ShowDialog();                     //shows the new login page form
            this.Close();                           //closes the register form that was hidden
        }