i am exporting databsae to excel file

Question

i am exporting database to excel file.

Design  as follows

Button(one button)

code as follows

using System;

using System.Data;

using System.Configuration;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Web.UI.HtmlControls;

using System.Data.SqlClient;

using System.Windows.Forms;

using Excel = Microsoft.Office.Interop.Excel;

public partial class _Default : System.Web.UI.Page 

{

    SqlConnection con = new SqlConnection("Server=(local);initial catalog=Rental;Trusted_Connection=True");

    protected void Page_Load(object sender, EventArgs e)

    {

    }

    protected void Button1_Click(object sender, EventArgs e)

    {

        SqlConnection con;

        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:\\csharp.net-informations.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();

            }

        }

    }

when i run i get this error:Use of unassigned local variable 'con'

Please  help from the above code what is the mistake.and send the code.

Thanks,

Rao