Compilare: main.cpp: In function 'int main()': main.cpp:104:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (a = 0; a < gr[s].size (); ++a) ~~^~~~~~~~~~~~~~~ main.cpp:105:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (b = a + 1; b < gr[s].size (); ++b) { ~~^~~~~~~~~~~~~~~ main.cpp:75:38: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("pirati.in", "r", stdin); ^ main.cpp:76:40: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("pirati.out", "w", stdout); ^