Compilare: user.cpp: In function ‘int main()’: user.cpp:68:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < stk.size(); i += 2) { ~~^~~~~~~~~~~~ user.cpp: In constructor ‘InputReader::InputReader(const char*)’: user.cpp:11:43: 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:34:47: 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); ^