Compilare: main.cpp: In constructor 'ABString::ABString(int, int, std::__cxx11::string)': main.cpp:65:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < str.size(); i++) ~~^~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:145:35: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("abba.in", "r", stdin); ^ main.cpp:146:37: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("abba.out", "w", stdout); ^