Export to Excel functionality Using Office.Interop.excel referenc

public void ExporExcelusingOffice()
        {
            // creating Excel Application

            Microsoft.Office.Interop.Excel._Application app = new Microsoft.Office.Interop.Excel.Application();

            // creating new WorkBook within Excel application

            Microsoft.Office.Interop.Excel._Workbook workbook = app.Workbooks.Add(Type.Missing);

            // creating new Excelsheet in workbook

            Microsoft.Office.Interop.Excel._Worksheet worksheet = null;

            // see the excel sheet behind the program
            app.Visible = true;

            // get the reference of first sheet. By default its name is Sheet1.

            // store its reference to worksheet

            worksheet = (Microsoft.Office.Interop.Excel.Worksheet)workbook.Sheets["Sheet1"];

            worksheet = (Microsoft.Office.Interop.Excel.Worksheet)workbook.ActiveSheet;

            // changing the name of active sheet

            worksheet.Name = "Exported from gridview";


            // storing header part in Excel

            for (int i = 1; i < grdViewYMP.Columns.Count + 1; i++)
            {
                worksheet.Cells[1, i] = grdViewYMP.HeaderRow.Cells[i - 1].Text.Trim();
            }

            DataTable dtYMP = ViewState["dtYMP"] as DataTable;


            // storing Each row and column value to excel sheet

            for (int i = 0; i < grdViewYMP.Rows.Count - 1; i++)
            {
                for (int j = 0; j < grdViewYMP.Columns.Count; j++)
                {
                    worksheet.Cells[i + 2, j + 1] = dtYMP.Rows[i][j].ToString();
                    //worksheet.Cells[i + 2, j + 1] = grdViewYMP.Rows[i].Cells[j].Text;
                }
            }

            // save the application
            object misValue = System.Reflection.Missing.Value;
            // workbook.SaveAs("c:\\output.xls", Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Microsoft.Office.Interop.Excel.XlSaveAsAccessMode.xlExclusive, Type.Missing, Type.Missing, Type.Missing, Type.Missing);
            workbook.SaveAs("c:\\YMPoutput.xlsx", Microsoft.Office.Interop.Excel.XlFileFormat.xlExcel9795, misValue, misValue, misValue, misValue, Microsoft.Office.Interop.Excel.XlSaveAsAccessMode.xlShared, misValue, misValue, misValue, misValue, misValue);
            // Exit from the application

            app.Quit();

        }