How to export a gridview to excel by using crystal report in ASP.NET C#?

protected void ExportToExcel()
{
    DataTable dt = new DataTable();

    GridView grdvTemp = new GridView();

    dt.Columns.Add("emp_number");
    dt.Columns.Add("emp_name");
    dt.Columns.Add("ntl_description");
    dt.Columns.Add("emp_SSN");
    dt.Columns.Add("emp_salary");
    dt.Columns.Add("dpt_name");
    dt.Columns.Add("emp_phone");
    dt.Columns.Add("emp_jobTitle");

    foreach(GridViewRow row in grdvEmployees.Rows)
    {
        DataRow dr = dt.NewRow();
        dr[0] = row.Cells[0].Text;
        dr[1] = row.Cells[1].Text;
        dr[2] = row.Cells[2].Text;
        dr[3] = row.Cells[3].Text;
        dr[4] = row.Cells[4].Text;
        dr[5] = row.Cells[5].Text;
        dr[6] = row.Cells[6].Text;
        dr[7] = row.Cells[7].Text;
        dt.Rows.Add(dr);
    }

    grdvTemp = grdvEmployees;
    grdvTemp.DataSource = null;
    grdvTemp.DataBind();
    grdvTemp.Columns.RemoveAt(8);
    grdvTemp.DataSource = dt;
    grdvTemp.DataBind();

    Response.Clear();
    Response.Buffer = true;
    Response.ClearContent();
    Response.ClearHeaders();
    Response.Charset = "";
    string FileName = "Vithal" + DateTime.Now + ".xls";
    StringWriter strwritter = new StringWriter();
    HtmlTextWriter htmltextwrtter = new HtmlTextWriter(strwritter);

    grdvTemp.HeaderRow.Style.Add("background-color", "#FFFFFF");
    foreach (TableCell tableCell in grdvTemp.HeaderRow.Cells)
        tableCell.Style["background-color"] = "#1C5E55";

    Response.Cache.SetCacheability(HttpCacheability.NoCache);
    Response.ContentType = "application/vnd.ms-excel";
    Response.AddHeader("Content-Disposition", "attachment;filename=" + FileName);
    grdvTemp.GridLines = GridLines.Both;
    grdvTemp.HeaderStyle.Font.Bold = true;
    grdvTemp.RenderControl(htmltextwrtter);
    Response.Write(strwritter.ToString());
    Response.End();
}