Compilare: user.cpp: In function ‘int main()’: user.cpp:27:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (D.size() >= L && D.size() <= U) ^ user.cpp:27:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (D.size() >= L && D.size() <= U) ^ user.cpp:30:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (D.size() > U) ^ user.cpp:10:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sum2.in","r",stdin); ^ user.cpp:11:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sum2.out","w",stdout); ^ user.cpp:13:32: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d %d",&N,&L,&U); ^ user.cpp:19:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d",&X); ^