Compilare: main.cpp: In function 'int can(int)': main.cpp:22:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i < ans.size(); i++){ ~~^~~~~~~~~~~~ main.cpp:28:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (ans.size() == w && s.empty()){ ~~~~~~~~~~~^~~~ main.cpp: In function 'int main()': main.cpp:40:33: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("sume.in","r",stdin); ^ main.cpp:41:35: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("sume.out","w",stdout); ^