ISR Callback Alias

#include <iostream>
#include <cstdint>

using namespace std;

using ISRCallback = void (*)(int32_t);

void onError(int32_t code) {
    cout << "ERROR " << code;
}

void onComplete(int32_t code) {
    cout << "COMPLETE " << code;
}

int main() {
    int32_t mode, eventCode;
    if (!(cin >> mode >> eventCode)) return 0;

    ISRCallback cb = nullptr;

    if(mode == 1){
        cb = onError;
    }
    else if(mode == 2){
        cb = onComplete;
    }

    if(cb){
        cb(eventCode);
    }

    return 0;
}

Solving Approach