Compilare: user.cpp: In function ‘void write()’: user.cpp:12:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); i++) ^ user.cpp: In function ‘void read()’: user.cpp:25:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); i++) ^ user.cpp: In function ‘void qs(std::vector<int>&)’: user.cpp:35:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); i++) ^ user.cpp:36:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = i + 1; j < a.size(); j++) ^ user.cpp:55:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < x.size() / 2; i++) ^ user.cpp:57:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < z.size() / 2; i++) ^