Compilare: user.cpp: In function ‘void df(int, char)’: user.cpp:31:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < v[x].size(); j++) ^ user.cpp: In function ‘int main()’: user.cpp:38:44: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("psychtraining.in", "r", stdin); ^ user.cpp:39:46: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("psychtraining.out", "w", stdout); ^ user.cpp:40:27: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &n, &m); ^ user.cpp:42:69: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &x, &y), v[x].push_back(y), v[y].push_back(x); ^