You can start with C++14, because C++ is backward compatible. Basically, you will learn a superset of previous versions, so if your C++14 knowledge covers all t

You can start with C++14, because C++ is backward compatible. Basically, you will learn a superset of previous versions, so if your C++14 knowledge covers all the C++ code written before as well. For a cross-platform GUI library to develop Desktop applications I recommend wxWidgets or Qt. I prefer wxWidgets myself. To build GUI, I recommend wxFormBuilder. For games, well, there's a lot to choose from. It depends on what kind of games you want to make.