public void LayThang()
{
DateTime now = DateTime.Now;
txt_ngayBD.Text = now.ToLongDateString();
txt_NgayKT.Text = now.ToLongDateString();
int DoanhThu = int.Parse(tk.LayDoanhThu(now, now).ToString());
int TienNhap = int.Parse(tk.LayTienNhap(now, now).ToString());
BieuDO(DoanhThu, TienNhap);
}