Compilare: user.cpp: In function ‘int main()’: user.cpp:22:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0;i < a.size(); ++i){ ^ user.cpp:32:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < a.size(); ++i){ ^ user.cpp:42:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = a.size(); i < b.size(); ++i){ ^