cpp detect os

#include <iostream>
using namespace std;

int main() {
    #ifdef _WIN32
       cout << "This is Windows." << endl;
    #elif __linux__
       cout << "This is Linux." << endl;
    #elif __APPLE__
       cout << "This is MacOS." << endl;
    #else
       cout << "This is an unknown operating system." << endl;
    #endif

    return 0;
}