Compilare: user.cpp: In function ‘bool used(int)’: user.cpp:16:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<=s.size();++i) ^ user.cpp: In function ‘int haca(int, int)’: user.cpp:24:9: warning: unused variable ‘ok’ [-Wunused-variable] int ok=0; ^ user.cpp: In function ‘int main()’: user.cpp:44:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<=s.size();++i) ^