Had I stuck with C++ or even C, ... That’s about the simplest example. Make a button and close the program when you push it. The mainloop call handles the event loop common in GUI programs.

This is an example C++ GUI program for validating a license key. For convenience, the source code contains a demo account id and license key. The example app has been tested on Windows, Mac and Ubuntu ...

It is example of polymorphism in C++ with GUI. See polymorph_learning_try3.cpp. It has interface view.h that is common interface for gui widget objects button and checkbox. check_mouse function is ...