Compilare: user.cpp: In function ‘int main()’: user.cpp:30:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < l.size(); ++i) ^ user.cpp:43:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < r.size(); ++i) ^ user.cpp:16:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("pipe.out", "w", stdout); ^