Compilare: user.cpp: In function ‘int main()’: user.cpp:20:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i<n.length()) ^ user.cpp:30:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<b.size();i++) out<<b.at(i)<<" "; ^ user.cpp:14:6: warning: unused variable ‘a’ [-Wunused-variable] int a=0; ^