public float TinhTongTien(int maKH, Dictionary <int, int> hangmua)
{
float tong = 0;
foreach (int maHH in hangmua.Keys)
{
tong += _dalHangHoa.GetRow(maHH).DonGia *hangmua[maHH];
}
return(tong - _dalKhachHang.GetRow(maKH).SoDiem);
}