Writing into an excel file

You need to add reference to  Com component - Microsoft.excel.

Excel.ApplicationClass app = new Excel.ApplicationClass();

Excel.Workbook wk = app.Workbooks.Open("F:\\MyExcel.xls", 0, false, 5,"", "", true, Excel.XlPlatform.xlWindows, "\t", true, false,0, true,true,false);

Excel.Sheets sheets = wk.Worksheets;

Excel.Worksheet sheet1 = (Excel.Worksheet)sheets.get_Item(1);

try{
for (int i = 1; i <= dtEmployee.Rows.Count; i++)  //dtEmployee is a datatable containing data
{
        for (int j = 1; j <= dtEmployee.Columns.Count; j++)
         {
                sheet1.Cells[i, j] = dtEmployee.Rows[i-1][j-1];
          }
}
}
catch{
}
finally{

app.Workbooks.Close();
app.Quit();
}