Compilare: user.cpp: In function ‘void dfs(int)’: user.cpp:30:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j=i+1;j<sons.size();j++) ^ user.cpp:39:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<sons.size();i++) ^ user.cpp:40:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j=0;j<sons.size();j++) ^ user.cpp:42:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<sons.size();i++) ^ user.cpp:45:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j=i+1;j<sons.size();j++) ^ user.cpp: In function ‘int main()’: user.cpp:59:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("petsoft.in","r",stdin); ^ user.cpp:60:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("petsoft.out","w",stdout); ^ user.cpp:61:19: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d",&n); ^ user.cpp:64:26: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] v[x].push_back(i); ^