Board-Independent Status Indicator

#include <iostream>
using namespace std;

/*
Select exactly ONE hardware board at build time.
*/
// #define BOARD_TYPE_A
 #define BOARD_TYPE_B

// Abstract interface used by application code
class StatusIndicator {
public:
    virtual void toggle() = 0;
    virtual bool isOn() const = 0;
    virtual ~StatusIndicator() = default;
};

/*
TASK FOR LEARNER:

- Create TWO board-specific implementations of StatusIndicator
- Select exactly one using conditional compilation
- Enforce compile-time errors for invalid selections
- Implement the factory function below

DO NOT modify main()
*/
#if defined(BOARD_TYPE_A) && defined(BOARD_TYPE_B)
#error "Select only one hardware board"
#elif defined(BOARD_TYPE_A)
    class BoardTypeA : public StatusIndicator {
    private:
        bool status = false;
    public:
        virtual void toggle() override
        {
            status = !status;
        }
        virtual bool isOn() const override
        {
            return status;
        }
    };

    StatusIndicator& getStatusIndicator()
    {
        static BoardTypeA boardTypeA;
        return boardTypeA;
    }
#elif defined(BOARD_TYPE_B)
    class BoardTypeB : public StatusIndicator {
    private:
        bool status = false;
    public:
        virtual void toggle() override
        {
            status = !status;
        }
        virtual bool isOn() const override
        {
            return status;
        }
    };

    StatusIndicator& getStatusIndicator()
    {
        static BoardTypeB boardTypeB;
        return boardTypeB;
    }
#else
    #error Board not selected.
#endif

// Factory function declaration (not implemented here)
StatusIndicator& getStatusIndicator();

int main() {
    int n;
    cin >> n;

    StatusIndicator& indicator = getStatusIndicator();

    for (int i = 0; i < n; ++i) {
        int evt;
        cin >> evt;

        if (evt == 1) {
            indicator.toggle();
        }

        cout << (indicator.isOn() ? "STATUS=ON\n" : "STATUS=OFF\n");
    }

    return 0;
}

Solving Approach