appending to an existing excel file
<p>I have this function which writes and saves to an excel file. What I want to do now is append to that same existing excel file.This is the function:</p>

<pre><code>private void button8_Click(object sender, EventArgs e)//creates excel file and writes data to it
    {
        Excel.Application xlApp = new Microsoft.Office.Interop.Excel.Application();

        if (xlApp == null)
        {
            MessageBox.Show("Excel is not properly installed!!");
            return;
        }

        if (System.IO.File.Exists("cross_check.xls"))
        {



        }
        else
        {


            Excel.Workbook xlWorkBook;
            Excel.Worksheet xlWorkSheet;
            object misValue = System.Reflection.Missing.Value;

            xlWorkBook = xlApp.Workbooks.Add(misValue);
            xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);
            IndexProp += 1; 
            xlWorkSheet.Cells[IndexProp, 1] = comboBox2.Text;
            xlWorkSheet.Cells[IndexProp, 2] = textBox5.Text;
            xlWorkSheet.Cells[IndexProp, 3] = textBox2.Text;
            xlWorkSheet.Cells[IndexProp, 4] = comboBox3.Text;
            xlWorkSheet.Cells[IndexProp, 5] = textBox3.Text;
            xlWorkSheet.Cells[IndexProp, 6] = comboBox1.Text;


            xlWorkBook.SaveAs(@"cross_check.xls", Excel.XlFileFormat.xlWorkbookNormal, misValue, misValue, misValue, misValue, Excel.XlSaveAsAccessMode.xlExclusive, misValue, misValue, misValue, misValue, misValue);
            xlWorkBook.Close(true, misValue, misValue);
            xlApp.Quit();

            Marshal.ReleaseComObject(xlWorkSheet);
            Marshal.ReleaseComObject(xlWorkBook);
            Marshal.ReleaseComObject(xlApp);

            MessageBox.Show("Excel file created succcessfully");
        }

    }
}
</code></pre>

<p>This particular block is checking for the file if it exists and then does the append operation if it exists. How do I do this? </p>

<pre><code> if (System.IO.File.Exists("cross_check.xls"))
        {



        }
</code></pre>