protected void Page_Load(object sender, EventArgs e)
{
   if (!IsPostBack)
   {
      //  Tworzymy dwuwymiarow tablic dla listy.
      //  Pierwszy wymiar zawiera tytu ksiki.
      //  Drugi wymiar zawiera numer ISBN.
      string[,] books = {
         {"Programming C#","0596001177"},
         {"Programming Visual Basic .NET","0596004389"},
         {"Programming .NET Windows Applications","0596003218"},
         {"Programming ASP.NET","0596001711"},
         {"WebClasses From Scratch","0789721260"},
         {"Teach Yourself C++ in 21 Days","067232072X"},
         {"Teach Yourself C++ in 10 Minutes","067231603X"},
         {"XML & Java From Scratch","0789724766"},
         {"Complete Idiot's Guide to a Career in Computer Programming",
"0789719959"},
         {"XML Web Documents From Scratch","0789723166"},
         {"Clouds To Code","1861000952"},
         {"C++: An Introduction to Programming","1575760614"},
         {"C++ Unleashed","0672312395"}
      };

      //  W tym miejscu zapeniamy list.
      for (int i = 0; i < books.GetLength(0); i++)
      {
         //  Dodajemy zarwno wartoi Text, jak i Value.
         ddl.Items.Add(new ListItem(books[i, 0], books[i, 1]));
      }
   }
}

protected void ddl_SelectedIndexChanged(object sender, EventArgs e)
{
   //  Sprawdzamy, czy cokolwiek zostao zaznaczone.
   if (ddl.SelectedIndex != -1)
   {
      lblDdl.Text = ddl.SelectedItem.Text + " ---> ISBN: " +
         ddl.SelectedValue;
   }
}
