Compilare: main.cpp: In function 'std::__cxx11::string rec(char, char)': main.cpp:37:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i <= len && p < r.length(); ++i){ ~~^~~~~~~~~~~~ main.cpp:51:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] }while(ok && p < r.length()); ~~^~~~~~~~~~~~