SQL to XLS

using System.Data;
using System.Data.SqlClient;
using System.IO;

public partial class Sql2Xl : System.Web.UI.Page
{
    SqlConnection cn = new SqlConnection("data source=SRIKANTA-PC\\SQLEXPRESS;initial catalog=adi;user id=sa;password=banka");
    protected void Page_Load(object sender, EventArgs e)
    {
        if (ConnectionState.Closed == cn.State)
        {
            cn.Open();
        }

    }

   
    protected void Button1_Click(object sender, EventArgs e)
    {
        DataSet ds = new DataSet();
        SqlDataAdapter da = new SqlDataAdapter("select * from student", cn);
        da.Fill(ds);
        ds.WriteXml(Server.MapPath(".") + "/abc.xml");

        File.Move(Server.MapPath(".") + "/abc.xml", Server.MapPath(".") + "/demo.xls");

       
    }
}