Compilare: main.cpp: In function 'bool f(std::__cxx11::string, char)': main.cpp:24:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0; j < a.size(); j++) { ~~^~~~~~~~~~ main.cpp: In function 'int eval(int)': main.cpp:38:45: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while('0' <= s[i] && s[i] <= '9' && i < s.size()) ~~^~~~~~~~~~ main.cpp:42:53: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(nr = eval(p + 1); f(priority[p], s[i]) && i < s.size(); nr = nr2) ~~^~~~~~~~~~