private void cmbLoaiPhong_SelectedIndexChanged(object sender, EventArgs e)
        {
            List <PhongDTO> ldg  = RoomBUS.LoadDonGia("A");
            List <PhongDTO> ldg1 = RoomBUS.LoadDonGia("B");
            List <PhongDTO> ldg2 = RoomBUS.LoadDonGia("C");

            if (cmbLoaiPhong.Text == "A")
            {
                txtDonGia.Text = string.Format("{0:0,0 VNĐ}", ldg[0].DonGia.Value);
            }
            if (cmbLoaiPhong.Text == "B")
            {
                txtDonGia.Text = string.Format("{0:0,0 VNĐ}", ldg1[0].DonGia.Value);
            }
            if (cmbLoaiPhong.Text == "C")
            {
                txtDonGia.Text = string.Format("{0:0,0 VNĐ}", ldg2[0].DonGia.Value);
            }
        }