try
            {
                string kaynak = Directory.GetCurrentDirectory() + "xxx.xls";
                Excel.Application xl = new Excel.Application();
                Excel.Workbook book = (Excel.Workbook)xl.ActiveWorkbook;
                book=(Excel.Workbook)(xl.Workbooks.Open(kaynak, Type.Missing, Type.Missing,      Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing,
                    Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing));

                Excel.Sheets sheet = book.Worksheets;
                Excel.Worksheet worksheet = (Excel.Worksheet)sheet.get_Item(3);

                worksheet.Cells[5,"A"]="ismail";
                book.Save();
                xl.Quit() ;
            }
            
            catch(Exception msg){
                MessageBox.Show(msg.Message);
            }