Compilare: user.cpp: In function ‘int main()’: user.cpp:14:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();i++) ~^~~~~~~~~ user.cpp:20:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();i++) ~^~~~~~~~~ user.cpp:19:13: warning: unused variable ‘ok’ [-Wunused-variable] int ok=1,nr=0; ^~