Compilare: user.cpp: In function ‘void shuffle_it(std::vector<int>&)’: user.cpp:49:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<v.size();i++) swap(v[i],v[rng.next(v.size())]); ^ user.cpp: In constructor ‘InputReader::InputReader(const char*)’: user.cpp:58:47: warning: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fread(buffer, SIZE, 1, input_file); ^ user.cpp: In member function ‘void InputReader::advance()’: user.cpp:81:51: warning: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fread(buffer, SIZE, 1, input_file); ^