Compilare: main.cpp: In function 'std::vector<bool> solve(std::vector<bool>)': main.cpp:11:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i < a.size(); ++i) { ~~^~~~~~~~~~ main.cpp:15:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = i + i; j < a.size(); j += i) { ~~^~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:42:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < v.size(); ++i) { ~~^~~~~~~~~~