Compilare: user.cpp: In function ‘void solve(int)’: user.cpp:15:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<V[x].size();++i) ^ user.cpp: In function ‘int main()’: user.cpp:26:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("rays.in","r",stdin); ^ user.cpp:27:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("rays.out","w",stdout); ^ user.cpp:29:19: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d",&n); ^ user.cpp:32:35: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d%d",&X,&Y1,&Y2); ^