Compilare: user.cpp: In function ‘int main()’: user.cpp:17:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<s.size();++j) ^ user.cpp:20:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<s.size();++j) ^ user.cpp:30:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<s.size();++j) ^ user.cpp:33:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<s.size();++j) ^