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:26:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); i++) ^ user.cpp: In function ‘std::vector<int> qs(std::vector<int>)’: user.cpp:38:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); i++) ^ user.cpp:49:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < y.size(); i++) ^ user.cpp:51:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < z.size(); i++) ^