Compilare: main.cpp: In function 'std::__cxx11::string eval(int&, std::__cxx11::string&)': main.cpp:11:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (it >= s.size()) ~~~^~~~~~~~~~~ main.cpp:15:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (it < s.size() && isalpha(s[it])) ~~~^~~~~~~~~~ main.cpp:21:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (it >= s.size()) ~~~^~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:81:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); i++) ~~^~~~~~~~~~