Compilare: main.cpp: In function 'std::__cxx11::string solve()': main.cpp:11:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (i >= s.size()) ~~^~~~~~~~~~~ main.cpp:14:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (isalpha(s[i]) && i < s.size()) { ~~^~~~~~~~~~ main.cpp:19:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (isdigit(s[i]) && i < s.size()) { ~~^~~~~~~~~~