Compilare: user.cpp: In function ‘int main()’: user.cpp:14:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<s.size();++i) ^ user.cpp:33:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<s.size();++i) ^ user.cpp:58:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<s.size();++i) ^ user.cpp:62:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<s.size();++i) ^