These are C++ versions of some of the C demos that are distributed with GTK.
You will probably find that they are easier to understand, because C++
allows much clearer organisation and reuse of code.

The gtk-demo contains multiple demos of functionality and APIs that are
new in gtk-4.0, and it shows the source code of the demos it is running.

There are more C++ demos in the gtkmm tutorial,
https://gnome.pages.gitlab.gnome.org/gtkmm-documentation
https://gitlab.gnome.org/GNOME/gtkmm-documentation
