private void add_recep_button_Click(object sender, EventArgs e)
        {
            if (nameTextBox.Text == "" || usernameTextBox.Text == "" || passwordTextBox.Text == "" || ((!maleRadioButton.Checked) && (!femaleRadioButton.Checked)))
            {
                MessageBox.Show("Please, insert at least the receptionist name, username, password, gender, age and salary.");
            }
            else
            {
                int r = controllerObj.A_AddReceptionist(nameTextBox.Text.ToString(),
                                                        usernameTextBox.Text.ToString(),
                                                        passwordTextBox.Text.ToString(),
                                                        maleRadioButton.Checked ? "M" : "F",
                                                        (int)ageNumericUpDown.Value,
                                                        mobileNumTextBox.Text.ToString(),
                                                        addressTextBox.Text.ToString(),
                                                        (int)salaryNumericUpDown.Value);

                if (r > 0)
                {
                    MessageBox.Show("Receptionist added successfully.");
                    DataTable dt1 = controllerObj.SelectReceptionistIDsNames();
                    recepsComboBox.DataSource    = dt1;
                    recepsComboBox.DisplayMember = "Name";
                    recepsComboBox.ValueMember   = "RecID";
                }
                else
                {
                    MessageBox.Show("Error in adding receptionist.");
                }
            }
        }