private void btnBaoCao_Click(object sender, EventArgs e) { dgvDanhSach.DataSource = SachBUS.BaoCaoDoanhThu(dtkNgay.Value); Custom(); dgvDanhSach.ClearSelection(); long TongTien = 0; for (int i = 0; i < dgvDanhSach.RowCount; i++) { TongTien = TongTien + Int64.Parse(dgvDanhSach.Rows[i].Cells[3].Value.ToString()); } txtTongtien.Text = String.Format("{0:0,0}", TongTien); }