Export to excel in asp.net?

private void ExportGridView()
    {
        //To make the last row unbold//
        //int j = gvScoreList.Rows[0].Cells.Count;
        int i = gvMark.Rows.Count;
        //foreach (GridViewRow row in gvSalaryStatement.Rows)
        //{
        //gvFeeReport.Rows[i - 1].Cells[j - 2].Text = "Total";
        //}
        if (i > 0)
        {
            btnExportToWord.Visible = true;
            btnExportToExcel.Visible = true;
            string attachment = "attachment; filename=File.xls";
            Response.ClearContent();
            Response.AddHeader("content-disposition", attachment);
            Response.ContentType = "application/ms-excel";
            StringWriter sw = new StringWriter();
            HtmlTextWriter htw = new HtmlTextWriter(sw);
            //gvScoreList.RenderControl(htw);
            //lblFailed.RenderControl(htw);
            pnlExport.RenderControl(htw);
            Response.Write(sw.ToString());
            Response.End();
        }
        else
        {
            btnExportToWord.Visible = false;
            btnExportToExcel.Visible = false;
        }
    }