Compilare: main.cpp: In function 'bool operator==(const iterator&, const string&)': main.cpp:38:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); ++i) { ~~^~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:170:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < n; ++i) { ~~^~~ main.cpp: In function 'Token next_token(std::__cxx11::basic_string<char>::iterator&)': main.cpp:85:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ main.cpp: In function 'bool eval(Node*)': main.cpp:157:1: warning: control reaches end of non-void function [-Wreturn-type] } ^