Compilare: user.cpp: In function ‘int main()’: user.cpp:20:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i<n.length(); i++) ^ user.cpp:27:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i<n.length(); i++) ^ user.cpp:30:42: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = i+1; j<n.length(); j++) ^