Things like SDL2 or SFML give you a plain canvas where you can draw anything you like. Been a while since I worked with these, so you may want to check how difficult it is to draw text on them.
Another option is of course the standard GUI toolkit of the platform of choice. If you want to be portable across platforms, that may be a bit tricky though.
I am not sure why you settled on C++. Being text-based it sounds like overkill, sort of using an F1 car to drive to the local grocery for doing some shopping. Without knowing what's inside the game, my first guess would be that Python is a feasible alternative which gives you options like PyGame. Python can also be used for making a GUI application, at least for Unix, so I am guessing it can also handle Windows GUI.