Compilare: main.cpp: In function 'bool ok(std::__cxx11::string)': main.cpp:13:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < n.length(); ++i) ~~^~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:24:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < cod.length(); ++i) ~~^~~~~~~~~~~~~~