how to get data in combobox value through

<asp:DropDownList AutoPostBack="true" ID="dd1" runat="server" OnSelectedIndexChanged="dd_select_changed">

       </asp:DropDownList>
       <asp:DropDownList ID="dd2" runat="server">
       </asp:DropDownList>
       <asp:Label ID="label1" runat="server"></asp:Label>
       <asp:Label ID="label2" runat="server"></asp:Label>
       <asp:Label ID="label3" runat="server"></asp:Label>

 protected void Page_Load(object sender, EventArgs e)
    {
        connection();
        string sql = "select * from Customer ";
        cmd = new SqlCommand(sql, conn);
        da = new SqlDataAdapter(cmd);
        da.Fill(ds);

           
            for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
            {
                dd1.DataSource = ds.Tables[0];
                dd1.DataBind();
                dd1.DataTextField = "CustomerName";//Colmn  name of custmer name in database table
                dd1.DataValueField = "CustomerId";//Colmn  name of custmer name in database table
                Label1.Text = ds.Tables[0].Rows[i]["CustomerAddress"].ToString();
            }
   }

 public void connection()
    {
        string sqlcon = System.Configuration.ConfigurationManager.AppSettings["conn"];
        conn=new SqlConnection(sqlcon);
        conn.Open();
    }

protected void dd_select_changed(object sender, EventArgs e)
    {
        connection();
        string sql = "select * from Customer where CustomerId='"+ Convert.ToInt32(dd1.SelectedItem.Value.ToString()) + "' ";
        cmd = new SqlCommand(sql, conn);
        da = new SqlDataAdapter(cmd);
        da.Fill(ds);
            Label1.Text = ds.Tables[0].Rows[0]["CustomerAddress"].ToString();
            Label2.Text = ds.Tables[0].Rows[0]["CustomerMobile"].ToString();
            Label3.Text = ds.Tables[0].Rows[0]["CustomerCity"].ToString();
    }