Compilare: main.cpp: In function 'bool prefix(std::__cxx11::string&, std::__cxx11::string&)': main.cpp:19:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size (); i++) ~~^~~~~~~~~~~ main.cpp: In function 'void solve(std::__cxx11::string&)': main.cpp:67:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (mid.size () == n) ~~~~~~~~~~~~^~~~ main.cpp:69:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (mid.size () > n) { ~~~~~~~~~~~~^~~ main.cpp: In function 'int main()': main.cpp:86:36: 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:87:38: 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); ^