Compilare: main.cpp: In function 'std::__cxx11::string add(std::__cxx11::string, std::__cxx11::string)': main.cpp:9:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (A.size() < k) A.push_back('0'); ~~~~~~~~~^~~ main.cpp:10:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (B.size() < k) B.push_back('0'); ~~~~~~~~~^~~ main.cpp: In function 'std::__cxx11::string mul(std::__cxx11::string, int)': main.cpp:25:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0;i<A.size();i++){ ~^~~~~~~~~ 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("perm.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("perm.out","w",stdout); ^