DownLoad CSV file in Asp.net

 public void ExportToCsv(DataTable table, string name)
        {
            try
            {
                if (table.Rows.Count > 0)
                {
                    HttpContext context = HttpContext.Current;
                    context.Response.Clear();
                    foreach (DataColumn column in table.Columns)
                    {
                        context.Response.Write(column.ColumnName + ",");

                    }
                   context.Response.Write(Environment.NewLine);

                    foreach (DataRow row in table.Rows)
                    {

                        for (int i = 0; i < table.Columns.Count; i++)
                        {

                            context.Response.Write(row[i].ToString().Replace(",", string.Empty) + ",");

                        }

                        context.Response.Write(Environment.NewLine);

                    }

                    context.Response.ContentType = "text/csv";
                    context.Response.AppendHeader("Content-Disposition", "attachment; filename=" + name + ".csv");
                    context.Response.End();

                }
            }
}

Create CSV file in Asp.net function

        protected void Button1_Click(object sender, EventArgs e)
        {
            try
            {
                ds = clpl.FetchSnapdealupdateFeed(1, 5);
                if (ds != null)
                {
                    if (ds.Tables.Count > 0)
                    {
                        if (ds.Tables[0].Rows.Count > 0)
                        {
                            // var dataTable = GetData();
                            StringBuilder builder = new StringBuilder();
                            List<string> columnNames = new List<string>();
                            List<string> rowss = new List<string>();

                            foreach (DataColumn column in ds.Tables[0].Columns)
                            {
                                columnNames.Add(column.ColumnName);
                            }

                            builder.Append(string.Join(",", columnNames.ToArray())).Append("\n");

                            foreach (DataRow row in ds.Tables[0].Rows)
                            {
                                List<string> currentRow = new List<string>();

                                foreach (DataColumn column in ds.Tables[0].Columns)
                                {
                                    object item = row[column];

                                    currentRow.Add(item.ToString());
                                }

                                rowss.Add(string.Join(",", currentRow.ToArray()));
                            }

                            builder.Append(string.Join("\n", rowss.ToArray()));

                            string Year = DateTime.Now.Year.ToString();
                            string Month = DateTime.Now.Month.ToString();
                            string Day = DateTime.Now.Day.ToString();

                            if (Day.Length == 1) { Day = '0' + Day; }
                            if (Month.Length == 1) { Month = '0' + Month; }
                            string spathTime = Day + "-" + Month + "-" + Year;
                            using (StreamWriter sw = new StreamWriter(System.Web.Hosting.HostingEnvironment.ApplicationPhysicalPath.ToString() + "snapdealfile/" + spathTime + "_snap.csv", true))
                            {
                                sw.WriteLine(builder.ToString());
                                sw.Flush();
                                sw.Close();
                                Response.Write("Create Succssefuly");

                            }
                        }
                    }
                }
            }
}

Export a DataTable to Excel in ASPNET

http://madskristensen.net/post/Export-a-DataTable-to-Excel-in-ASPNET