private void btnLogin_Click(object sender, RoutedEventArgs e)
        {
            if (combobox.SelectedItem == null)
            {
                MessageBox.Show("Please choose an option");
            }
            else if (combobox.SelectedItem.Equals("Staff"))
            {
                /*StaffWindow objStaffWindow = new StaffWindow();
                 * objStaffWindow.Show();
                 * this.Close();*/

                MySqlConnection conn = DBConnect.connectToDb();
                try
                {
                    string          q          = "select * from user.staff where staff_id='" + textboxUsername.Text + "' and staff_password='******';";
                    MySqlCommand    MyCommand2 = new MySqlCommand(q, conn);
                    MySqlDataReader MyReader2;
                    MyReader2 = MyCommand2.ExecuteReader();     // Here our query will be executed and data saved into the database.
                    if (MyReader2.Read())
                    {
                        MessageBox.Show("You have succesfully logged in");
                        StaffWindow objStaffWindow = new StaffWindow();
                        objStaffWindow.Show();
                        objStaffWindow.loginAsStaff.Text = textboxUsername.Text;
                        this.Close();
                    }
                    else
                    {
                        MessageBox.Show("Username or password do not match");
                    }
                    conn.Close();
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
            }

            else if (combobox.SelectedItem.Equals("Doctor"))
            {
                MySqlConnection conn = DBConnect.connectToDb();
                try
                {
                    string          q          = "select * from user.doctor where id='" + textboxUsername.Text + "' and password='******';";
                    MySqlCommand    MyCommand2 = new MySqlCommand(q, conn);
                    MySqlDataReader MyReader2;
                    MyReader2 = MyCommand2.ExecuteReader();
                    if (MyReader2.Read())
                    {
                        DoctorWindow objDoctorWindow = new DoctorWindow();
                        objDoctorWindow.loginAsDoctor.Text = textboxUsername.Text;
                        objDoctorWindow.Show();
                        this.Close();
                    }
                    else
                    {
                        MessageBox.Show("Username or password do not match");
                    }
                    conn.Close();
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
            }
            else if (combobox.SelectedItem.Equals("Adminstrator"))
            {
                MySqlConnection conn = DBConnect.connectToDb();
                try
                {
                    string          q          = "select * from user.admin where username='******' and password='******';";
                    MySqlCommand    MyCommand2 = new MySqlCommand(q, conn);
                    MySqlDataReader MyReader2;
                    MyReader2 = MyCommand2.ExecuteReader();
                    if (MyReader2.Read())
                    {
                        MessageBox.Show("You have succesfully logged in");
                        AdminWindow objAdminWindow = new AdminWindow();
                        objAdminWindow.Show();
                        this.Close();
                    }
                    else
                    {
                        MessageBox.Show("Username or password do not match");
                    }
                    conn.Close();
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
            }
        }