Compilare: user.cpp: In function ‘int main()’: user.cpp:63:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j=0;j<V[i].size();++j) ^ user.cpp: In member function ‘void InputReader::advance()’: user.cpp:32:51: 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); ^ user.cpp: In constructor ‘InputReader::InputReader(const char*)’: user.cpp:10:47: 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); ^