Compilare: user.cpp: In function ‘void dfs(int)’: user.cpp:14:48: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(register int i = 0; i < G[source].size(); ++ i) ^ user.cpp: In function ‘int main()’: user.cpp:21:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("dfs.in", "r", stdin); ^ user.cpp:22:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("dfs.out", "w", stdout); ^ user.cpp:24:27: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &N, &M); ^ user.cpp:27:31: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &a, &b); ^