So I've gone with a somewhat singleton approach to my game class:

#include "myGame.h"

int main () {
    myGame game;
    return game.Execute();
}

But now I need to define a class that accesses variables in the instance of myGame.

class MotionState {
    public:
    virtual void setWorldTransform (...) {
        VariableFromMyGameClass++;            //<-- !?
        ...}
};

I'm trying to integrate this class into my project from an example that just uses globals. How can I access variables of myGame class in the definition of new classes? Should I give up on my singleton approach?