Compilare: user.cpp: In function ‘void ctc(int, int)’: user.cpp:18:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0, f; i < V[n].size(); i++) ^ user.cpp: In function ‘int main()’: user.cpp:71:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < CTC[c].size(); i++) ^ user.cpp:49:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("ctc.in", "r", stdin); ^ user.cpp:50:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("ctc.out", "w", stdout); ^ user.cpp:52:27: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf ("%d%d", &N, &M); ^ user.cpp:56:31: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf ("%d%d", &a, &b); ^