protected void ExportToExcel(object sender, EventArgs e)
{
      DataTable dt = new DataTable();
      dt.Columns.Add("Number");
      dt.Columns.Add("Text");
      dt.Columns.Add("Currency");
      dt.Columns.Add("Date");
      dt.Columns.Add("Percentage");
      dt.Rows.Add("546", "This is Text", "546", "16/8/2011", "25");
      dt.Rows.Add("5461", "This is again Text", "5462", "20/9/2011", "35");

      //Double dimensional array to keep style name and style
      string[,] styles = { { "number", "0\\.00;" }, { "text", "\\@;" }, { "currency", "\\[\\$\\$\\-\\409\\]\\#\\,\\#\\#0\\.00;" }, { "date", "mm\\-dd\\-yy\\;\\@;" }, { "percent", "0\\.00\\%;" } };

      //Dummy GridView to hold data to be exported in excel
      System.Web.UI.WebControls.GridView gvExport = new System.Web.UI.WebControls.GridView();
      gvExport.AllowPaging = false;
      gvExport.DataSource = dt;
      gvExport.DataBind();

      StringWriter sw = new StringWriter();
      HtmlTextWriter hw = new HtmlTextWriter(sw);

      int cnt = styles.Length / 2;

      for (int i = 0; i < gvExport.Rows.Count; i++)
      {
            for (int j = 0; j < cnt; j++)
            {
                  //Apply style to each cell
                  gvExport.Rows[i].Cells[j].Attributes.Add("class", styles[j, 0]);
            }
      }

      gvExport.RenderControl(hw);
      StringBuilder style = new StringBuilder();
      style.Append("<style>");
      for (int j = 0; j < cnt; j++)
      {
            style.Append("." + styles[j, 0] + " { mso-number-format:" + styles[j, 1] + " }");
      }

      style.Append("</style>");
      Response.Clear();
      Response.Buffer = true;
      Response.AddHeader("content-disposition", "attachment;filename=Export.xls");Response.Charset = "";
      Response.ContentType = "application/vnd.ms-excel";
      Response.Write(style.ToString());
      Response.Output.Write(sw.ToString());
      Response.Flush();
      Response.End();
}

Below line of code in above statements sets the style of excel. The styling of first column will be number, second will be text, third will currency, fourth will be date and fifth will be percent.

  string[,] styles = { { "number", "0\\.00;" }, { "text", "\\@;" }, { "currency", "\\[\\$\\$\\-\\409\\]\\#\\,\\#\\#0\\.00;" }, { "date", "mm\\-dd\\-yy\\;\\@;" }, { "percent", "0\\.00\\%;" } };

Now let's see how we can get the styling code.

Step 1: Open Excel and type any number in any cell.

Step 2: Right click and select Format Cells

Step 3: Select Currency from number tab.

Step 4: Change the Symbol dropdownlist to $ English (U.S.)