Well I would recommend you have a basic understanding of:
-The essentials Logic, loops, pointers, arrays, references, functions, and all the basics.
-Classes and Structs
>>Along with classes and structs you should understand inheritance (simply because it makes writing the code degrees easier) and the topics that come with it.
-You will need some knowledge of how to actually address the screen in some way other than the console, so look into libraries like SDL (my favorite), or SFML, or Allegro, or a platform specific API, such as *shudder* WinAPI.
Basically you should be able to do anything inside c++ so you have the ability to do anything within the game realm.
Now I hate to blatantly advertise myself like this, but I do know somewhat concerning what I'm talking about and check out my game here
http://sourceforge.net/projects/ultiscroll/