Gridview to MS office or Excel

Response.Clear();

            Response.Buffer = true;

            Response.AddHeader("content-disposition",

             "attachment;filename=GridViewExport.csv");

            Response.Charset = "";

            Response.ContentType = "application/text";



            GridView1.AllowPaging = false;

            GridView1.DataBind();



            StringBuilder sb = new StringBuilder();

            for (int k = 0; k < GridView1.Columns.Count; k++)
            {

                //add separator

                sb.Append(GridView1.Columns[k].HeaderText + ',');

            }

            //append new line

            sb.Append("\r\n");

            for (int i = 0; i < GridView1.Rows.Count; i++)
            {

                for (int k = 0; k < GridView1.Columns.Count; k++)
                {

                    //add separator

                    sb.Append(GridView1.Rows[i].Cells[k].Text + ',');

                }

                //append new line

                sb.Append("\r\n");

            }

            Response.Output.Write(sb.ToString());

            Response.Flush();

            Response.End();

using System.IO;
using System.Text;

private void ExportDataTable(DataTable dt)
       {
           string attachment = "attachment; filename=a.xls";
           HttpContext.Current.Response.Clear();
           HttpContext.Current.Response.AddHeader("content-disposition", attachment);
           HttpContext.Current.Response.ContentType = "application/vnd.ms-excel";
           string sTab = "";
           foreach (DataColumn dc in dt.Columns)
           {
               HttpContext.Current.Response.Write(sTab + dc.ColumnName);
               sTab = "\t";
           }
           HttpContext.Current.Response.Write("\n");

           int i;
           foreach (DataRow dr in dt.Rows)
           {
               sTab = "";
               for (i = 0; i < dt.Columns.Count; i++)
               {
                   HttpContext.Current.Response.Write(sTab + dr[i].ToString());
                   sTab = "\t";
               }
               HttpContext.Current.Response.Write("\n");
           }
           HttpContext.Current.Response.End();
       }