Problem with installing Gtkada or gcc or or code Hello World Gtkada?

General
2

The simplest way is to use Alire. Try this:

alr init --bin my_gtk_app
cd my_gtk_app
alr with gtkada
# Edit src/my_gtk_app.adb
alr run

The my_gtk_app.adb could be as simple as this:

with Gtk.Main, Gtk.Window;

procedure Simple_Application is
   Window : Gtk.Window.Gtk_Window;
begin
   Gtk.Main.Init;
   Gtk.Window.Gtk_New (Window);
   Gtk.Window.Show (Window);
   Gtk.Main.Main;
end Simple_Application;