Compilare: user.cpp: In function ‘bool operator==(const iterator&, const string&)’: user.cpp:38:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); ++i) { ^ user.cpp: In function ‘int main()’: user.cpp:171:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < n; ++i) { ^ user.cpp: In function ‘Token next_token(std::basic_string<char>::iterator&)’: user.cpp:85:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ user.cpp: In function ‘bool eval(Node*)’: user.cpp:158:1: warning: control reaches end of non-void function [-Wreturn-type] } ^