Show Number formate Columns to Text formate in excel export in asp.net, C#

            string datestyle = @"<style> .nf{mso-number-format:\@;}</style>";

//add this string to your export data table

            HttpResponse Response = HttpContext.Current.Response;

            string filename = "Test" + "_" + System.DateTime.Now.ToString("MMddyy_hhmmss") + ".doc";

            Response.Clear();

            Response.AddHeader("content-disposition", "attachment;filename=" + filename);

            Response.Charset = "";

            Response.ContentType = "application/xls";

            System.IO.StringWriter WriteItem = new System.IO.StringWriter();

            System.Web.UI.HtmlTextWriter htmlText = newHtmlTextWriter(WriteItem);

            Response.Write(datestyle);

            Response.Write(strBuilder.ToString());

            Response.End();