Good work, pleasing UI (when it works). Please also compare with the excellent pythontutor.com website (it works with C++ too: http://pythontutor.com/cpp.html ).

Examples of differences I can see:

* pythontutor requires a backend and does not run entirely in the browser.

* pythontutor supports much more of C++ (i.e., has fewer limitations)

* shows pointers, heap and stack better.

But there are probably many more differences; would like to see a comparison among similar resources. Anyway, I think this sort of live visualization is indeed very useful; great work and please continue.