You need to double buffer the output. Create a bitmap in memory; copy from your frame to that bitmap, then draw your extra graphics on that bitmap. Then when it's done draw it to the screen in one blit. That's how you get rid of the flicker. Gdi+ will do it fine.

A good example of why you should use const: const int* GetA() const { return &m_a; } *GetA() = *GetB(); // compile error - use the Set function you numpty