Compilare: main.cpp: In function 'std::__cxx11::string sum(std::__cxx11::string, std::__cxx11::string)': main.cpp:8:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (A.size() < mx) A += '0'; ~~~~~~~~~^~~~ main.cpp:9:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (B.size() < mx) B += '0'; ~~~~~~~~~^~~~ main.cpp: In function 'int main()': main.cpp:52:32: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("zero.in","r",stdin); ^ main.cpp:53:34: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("zero.out","w",stdout); ^