private void export_excel()
        {

            Microsoft.Office.Interop.Excel._Application app = new Microsoft.Office.Interop.Excel.Application();
            Microsoft.Office.Interop.Excel._Workbook workbook = app.Workbooks.Add(Type.Missing);
            Microsoft.Office.Interop.Excel._Worksheet worksheet = null;
            app.Visible = true;
            worksheet = workbook.Sheets["Sheet1"];
            worksheet = workbook.ActiveSheet;
            worksheet.Name = "Exported from gridview";
            for (int i = 1; i < Grid1.Columns.Count + 1; i++)
            {
                worksheet.Cells[1, i] = Grid1.Columns[i - 1].HeaderText;
            }
            for (int i = 0; i < Grid1.Rows.Count - 1; i++)
            {
                for (int j = 0; j < Grid1.Columns.Count; j++)
                {
                    worksheet.Cells[i + 1, j + 1] = Grid1.Rows[i].Cells[j].Value.ToString();
                }
            }

            System.Windows.Forms.SaveFileDialog saveDlg = new System.Windows.Forms.SaveFileDialog();
            saveDlg.InitialDirectory = @"C:\";
            saveDlg.Filter = "Excel files (*.xlsx)|*.xlsx";
            saveDlg.FilterIndex = 0;
            saveDlg.RestoreDirectory = true;
            saveDlg.Title = "Export Excel File To";
            if (saveDlg.ShowDialog() == System.Windows.Forms.DialogResult.OK)
            {
                string path = saveDlg.FileName;
                workbook.SaveCopyAs(path);
                workbook.Saved = true;
                workbook.Close();
                app.Quit();
            }
        }