Adding a Frame class required some significant changes:

class Game
{
    class Frame
    {
        int rollOne=-1, rollTwo=0;
    public:
        bool Roll(int pins)
        {
            if (rollOne == -1) {
                rollOne = pins;
                return false;
            } else {
                rollTwo = pins;
                return true;
            }
        }
        int Sum() const { return rollOne + rollTwo; }
    };
    Frame frames[10];
    int currentFrame = 0;

public:
    void Roll(int pins)
    {
        if (pins<0 || pins>10)
            throw std::out_of_range("'pins' is out of range");
            
        if (frames[currentFrame].Roll(pins) == true)
            ++currentFrame;
    }
    int Score() const
    {
        int score = 0;
        for(const auto& frame : frames)
            score += frame.Sum();
        return score;
    }
};

I added the Frame class, which holds onto two pieces of data, rollOne and rollTwo. To distinguish when pins refers to the first roll or second, I initialize rollOne to -1. And there’s a Sum method to return the sum of the two rolls.

Now using it, we need to know when we’ve had two rolls and thus are past a frame boundary. The Frame::Roll method returns true when the frame is complete, and we can just increment the currentFrame counter.

All the tests pass. But maybe we can refactor some more. Writing raw loops, rather than using an appropriate <numeric> algorithm, is considered poor form.

Let’s make that change and then click Next