Compilare: user.cpp: In function ‘void prefix()’: user.cpp:21:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 1 ; i < A.size() ; ++i){ ^ user.cpp: In function ‘int main()’: user.cpp:37:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0 ; i < B.size() ; ++i){ ^ user.cpp:42:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(k == A.size()){ ^