Multiple sheet Excel Download c#

 private void writeDataToExcelFile(
         DataSet ds)
    {
        var workbook = new HSSFWorkbook();
        String sheetName = "Orignal";
        string filename = Convert.ToString(ds.Tables[0].Rows[0]["filename"]);
        for (int i = 0; i < ds.Tables.Count; i++)
        {
            DataTable dt = ds.Tables[i];
            if (dt.Rows.Count > 0)
            {
                if (i == 0)
                    sheetName = "Original";
                else sheetName = "plagiarism";
                var Sheet = workbook.CreateSheet(sheetName);

                int cols = 0;
                var myRow = Sheet.CreateRow(0);
                var style1 = workbook.CreateCellStyle();

                // cell background
                style1.FillBackgroundColor = NPOI.HSSF.Util.HSSFColor.VIOLET.index;

                // font color
                var font1 = workbook.CreateFont();
                font1.Color = NPOI.HSSF.Util.HSSFColor.BLUE.index;
                style1.SetFont(font1);


                foreach (DataColumn column in dt.Columns)
                {
                    var Cell = myRow.CreateCell(cols);
                    Cell.SetCellValue(column.ColumnName);
                    Cell.CellStyle = style1;
                    cols++;
                }


                for (int rowNum = 0; rowNum < dt.Rows.Count; rowNum++)
                {
                    myRow = Sheet.CreateRow(rowNum + 1);
                    for (int cellNum = 0; cellNum < dt.Columns.Count; cellNum++)
                    {
                        var Cell = myRow.CreateCell(cellNum);
                        Cell.SetCellValue(Convert.ToString(dt.Rows[rowNum][cellNum]));
                    }

                }
            }
        }
        using (var buffer = new MemoryStream())
        {
            workbook.Write(buffer);

            Response.ContentType = "application/vnd.ms-excel";
            Response.AddHeader("Content-Disposition", string.Format("attachment;filename={0}", "test.xls"));
            Response.Clear();
            Response.BinaryWrite(buffer.GetBuffer());
            Response.End();
        }


    }

Export multiple DataSets to multiple Excel sheets dynamically formatted according to the record's data type

   public string DataSetsToExcel(List<DataSet> dataSets, string fileName)

    {

        Microsoft.Office.Interop.Excel.Application xlApp =

                  new Microsoft.Office.Interop.Excel.Application();

        Workbook xlWorkbook = xlApp.Workbooks.Add(XlWBATemplate.xlWBATWorksheet);

        Sheets xlSheets = null;

        Worksheet xlWorksheet = null;

        foreach (DataSet dataSet in dataSets)

        {

            System.Data.DataTable dataTable = dataSet.Tables[0];

            int rowNo = dataTable.Rows.Count;

            int columnNo = dataTable.Columns.Count;

            int colIndex = 0;

            //Create Excel Sheets

            xlSheets = xlWorkbook.Sheets;

            xlWorksheet = (Worksheet)xlSheets.Add(xlSheets[1],

                           Type.Missing, Type.Missing, Type.Missing);

            xlWorksheet.Name = dataSet.DataSetName;

            //Generate Field Names

            foreach (DataColumn dataColumn in dataTable.Columns)

            {

                colIndex++;

                xlApp.Cells[1, colIndex] = dataColumn.ColumnName;

                xlWorksheet.Range[xlApp.Cells[1, colIndex],

           xlApp.Cells[1, colIndex]].Interior.Color = Microsoft.Office.Interop.Excel.XlRgbColor.rgbCornflowerBlue;

                xlWorksheet.Range[xlApp.Cells[1, colIndex],

      xlApp.Cells[1, colIndex]].Font.Bold = true;

                xlWorksheet.Range[xlApp.Cells[1, colIndex],

xlApp.Cells[1, colIndex]].Font.Color = Microsoft.Office.Interop.Excel.XlRgbColor.rgbAntiqueWhite;

            }

            object[,] objData = new object[rowNo, columnNo];

            //Convert DataSet to Cell Data

            for (int row = 0; row < rowNo; row++)

            {

                for (int col = 0; col < columnNo; col++)

                {

                    objData[row, col] = dataTable.Rows[row][col];

                }

            }

            //Add the Data

            Range range = xlWorksheet.Range[xlApp.Cells[2, 1], xlApp.Cells[rowNo + 1, columnNo]];

            range.Value2 = objData;

            //Format Data Type of Columns

            colIndex = 0;

            foreach (DataColumn dataColumn in dataTable.Columns)

            {

                colIndex++;

                string format = "@";

                switch (dataColumn.DataType.Name)

                {

                    case "Boolean":

                        break;

                    case "Byte":

                        break;

                    case "Char":

                        break;

                    case "DateTime":

                        format = "dd/mm/yyyy";

                        break;

                    case "Decimal":

                        format = "$* #,##0.00;[Red]-$* #,##0.00";

                        break;

                    case "Double":

                        break;

                    case "Int16":

                        format = "0";

                        break;

                    case "Int32":

                        format = "0";

                        break;

                    case "Int64":

                        format = "0";

                        break;

                    case "SByte":

                        break;

                    case "Single":

                        break;

                    case "TimeSpan":

                        break;

                    case "UInt16":

                        break;

                    case "UInt32":

                        break;

                    case "UInt64":

                        break;

                    default: //String

                        break;

                }

                //Format the Column accodring to Data Type

                xlWorksheet.Range[xlApp.Cells[2, colIndex],

                      xlApp.Cells[rowNo + 1, colIndex]].NumberFormat = format;

            }

        }

        //Remove the Default Worksheet

        ((Worksheet)xlApp.ActiveWorkbook.Sheets[xlApp.ActiveWorkbook.Sheets.Count]).Delete();

        /*

          foreach (Microsoft.Office.Interop.Excel.Range usedRange in xlWorksheet.Rows)

          {

           

                  usedRange.Cells.Interior.Color = Microsoft.Office.Interop.Excel.XlRgbColor.rgbCornflowerBlue;

                  break;

          }*/

        //Save

        if (File.Exists(HttpContext.Current.Server.MapPath("~/Excel/" + fileName + ".xls")))

            File.Delete(HttpContext.Current.Server.MapPath("~/Excel/" + fileName + ".xls"));

        xlWorkbook.SaveAs(HttpContext.Current.Server.MapPath("~/Excel/" + fileName + ".xls"),

            System.Reflection.Missing.Value,

            System.Reflection.Missing.Value,

            System.Reflection.Missing.Value,

            System.Reflection.Missing.Value,

            System.Reflection.Missing.Value,

            XlSaveAsAccessMode.xlNoChange,

            System.Reflection.Missing.Value,

            System.Reflection.Missing.Value,

            System.Reflection.Missing.Value,

            System.Reflection.Missing.Value,

            System.Reflection.Missing.Value);

        xlWorkbook.Close();

        xlApp.Quit();

        GC.Collect();

        return fileName;

    }

 http://www.codeproject.com/Articles/335589/Export-Multiple-Datasets-to-Multiple-Excel-sheets