fibonacci.vala

using Gtk;

public long fibonacci (int n)
{
    if (n < 2) {
        return n;
      } else {
        return (fibonacci(n - 1) + fibonacci(n - 2));
    }
}

public static int main (string[] args)
{
    Gtk.init (ref args);

    var window = new Window ();
    window.title = "Fibonacci GTK+";
    window.set_border_width (12);
    window.set_default_size (70, 70);
    window.set_position (Gtk.WindowPosition.CENTER);
    window.destroy.connect (Gtk.main_quit);

    var loop = new MainLoop();

    long result = 0;

    var headerbar = new HeaderBar ();
    var entry = new Entry ();
    var button = new Button.with_label ("Calcular");
    var label = new Label ("Resultado");
    var box = new Box (Orientation.VERTICAL, 0);

    headerbar.title = "Fibonacci GTK+";
    headerbar.show_close_button = true;

    box.pack_start (entry, false, true, 0);
    box.pack_start (label, false, true, 12);
    box.pack_start (button, false, true, 0);

    window.set_titlebar (headerbar);

    window.add (box);
    window.show_all ();

    /*** LOGICA ***/
    button.clicked.connect ( ()=> {
        result = fibonacci (int.parse (entry.get_text ()));
            label.set_label (result.to_string ());
        loop.quit();
    });

    loop.run ();

    Gtk.main ();
    return 0;
}