Compilare: user.cpp: In function ‘void dfs(int)’: user.cpp:11:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<m[x].size();++i) { ^ user.cpp: In function ‘void dfs2(int)’: user.cpp:23:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<n[x].size();++i) { ^ user.cpp: In function ‘void f(int, int)’: user.cpp:37:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<v[x].size();++i) { ^ user.cpp:44:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<v[x].size();++i) { ^ user.cpp: In function ‘int main()’: user.cpp:56:30: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("2sat.in","r",stdin); ^ user.cpp:57:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("2sat.out","w",stdout); ^ user.cpp:59:21: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&N,&M); ^ user.cpp:61:28: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&x,&y); ^