Compilare: main.cpp: In function 'int pref(std::__cxx11::string&, std::__cxx11::string&)': main.cpp:13:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < a.size () && i < b.size () && a[i] == b[i]) ~~^~~~~~~~~~~ main.cpp:13:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < a.size () && i < b.size () && a[i] == b[i]) ~~^~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:20:36: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("ratina.in", "r", stdin); ^ main.cpp:21:38: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("ratina.out", "w", stdout); ^ main.cpp:23:25: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf ("%d%d", &n, &m); ^