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...meaning #if #endif
- Enforce compile-time errors for invalid selections...#if defined()
- Implement the factory function below

DO NOT modify main()
*/

#if defined(BOARD_TYPE_A) && defined(BOARD_TYPE_B)
#error "Only one board can be defined";
#endif

#if !defined(BOARD_TYPE_A) && !defined(BOARD_TYPE_B)
#error "Atleast one board must be defined";
#endif

#if defined(BOARD_TYPE_A)

    class BoardAIndicator: public StatusIndicator{
        private:
            int state;

        public:
            void toggle() override{
                state = state ? 0:1;
            }

            bool isOn() const override {
                return state ? true : false;
            }
    };

    StatusIndicator& getStatusIndicator(){
        static BoardAIndicator board_a;
        return board_a;
    }

#elif defined(BOARD_TYPE_B)

    class BoardBIndicator: public StatusIndicator{
        private:
            int state;
        public:

            void toggle()override{
                state = state ? 0:1;
            }

            bool isOn() const override{
            return state ? true : false;
            }
    };

    StatusIndicator& getStatusIndicator(){
        static BoardBIndicator board_b;
        return board_b;
    }

#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