Compilare: user.cpp: In function ‘int main()’: user.cpp:63:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < answer.size() ;++i) ^ user.cpp:56:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("ciclueuler.in","r",stdin); ^ user.cpp:57:41: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("ciclueuler.out","w",stdout); ^ user.cpp: In function ‘void read()’: user.cpp:21:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&N,&M); ^ user.cpp:25:28: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&a,&b); ^