Compilare: user.cpp: In function ‘void read_data()’: user.cpp:33:29: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d\n", &N, &M); ^ user.cpp:35:62: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d\n", &a, &b), G[a].push_back(b), deg[b]++; ^ user.cpp: In function ‘int main()’: user.cpp:48:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sortaret.in", "rt", stdin); ^ user.cpp:49:42: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sortaret.out", "wt", stdout); ^