Exporting Database to Excel File

public partial class _Default : System.Web.UI.Page 
{
    SqlConnection con ;
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        con== new SqlConnection("Server=(local);initial catalog=Rental;Trusted_Connection=True");
        string sql = null;
        string data = null;
        int i = 0;
        int j = 0;

        Excel.Application xlapp;
        Excel.Workbook xlWorkBook;
        Excel.Worksheet xlWorksheet;
        object misvalue = System.Reflection.Missing.Value;

        xlapp = new Excel.ApplicationClass();
        xlWorkBook = xlapp.Workbooks.Add(misvalue);
        xlWorksheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);


        //cnn = new SqlConnection(connectionstring);
        con.Open();
        sql = "Select * from mis";
        SqlDataAdapter da = new SqlDataAdapter(sql, con);
        DataSet ds = new DataSet();
        da.Fill(ds);


        for (i = 0; i <= ds.Tables[0].Rows.Count - 1; i++)
        {
            for (j = 0; j <= ds.Tables[0].Columns.Count - 1; j++)
            {
                data = ds.Tables[0].Rows[i].ItemArray[j].ToString();
                xlWorksheet.Cells[i + 1, j + 1] = data;
            }
        }

        MessageBox.Show("Excel file created , you can find the file C:\\Documents and Settings\\narasiman\\Desktop\\Excel\\export.xls");

    }
        private void releaseObject(object obj)
        {
            try
            {
                System.Runtime.InteropServices.Marshal.ReleaseComObject(obj);
                obj = null;
            }
            catch (Exception ex)
            {
                obj = null;
                MessageBox.Show("Exception Occured while releasing object " + ex.ToString());
            }
            finally
            {
                GC.Collect();
            }
        }
    }