well that's just the basics of C programming language. It can't be compared with a real game's code. Printing a "hello world!" text into a console window is nothing compared to loading sprites, resources and/or dynamic graphics (may it be 2d or 3d) rendering.
well, on your side you OpenGL is probably easy for you to read coz you already have done it. But for a newbie in programming it'll just result into furstrations (mostly in C++). Coz there are somethings must be done in game which are not in a common windows application. one if it is jumping and moving images/objects to certain locations or coordinates on a screen.

the game dev tools i mentioned are not as what you think they are. Besides I learned openGL better using one of em than starting from scratch working with openGL functions. Ofcourse if you use these tools, you can only doo what is available in it, but most of the time there's no more you need than what these tools offers. But if required, yes they can be integrated to it (e.g. external libraries/resources). All of it depends on what game you'll develop and which platform(game genre) it is.