Compilare: user.cpp: In function ‘int main()’: user.cpp:15:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(s.size()<=n && s.size()!=0) ^ user.cpp:49:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=n-nr-1;i<s.size();++i) ^ user.cpp:75:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=n-nr+1;i<s.size();++i) ^