gcc (the gnu compiler) is free and good. Since you probably want an IDE to go with it, try DevC++ or Mingw studio on Windows (I don't know what IDEs are good on linux). Microsofts C++ compiler is excellent and available for free, but without the IDE. There might be free IDEs that can use it, but I don't know of any, try google. Intel's compiler is only free for linux IIRC.