Compilare: main.cpp: In function 'void add(std::__cxx11::string&, Node*)': main.cpp:22:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < str.size(); ++i){ ~~^~~~~~~~~~~~ main.cpp: In function 'void del(std::__cxx11::string&, Node*)': main.cpp:39:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < str.size(); ++i){ ~~^~~~~~~~~~~~ main.cpp: In function 'int apar(std::__cxx11::string&, Node*)': main.cpp:47:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < str.size(); ++i){ ~~^~~~~~~~~~~~ main.cpp: In function 'int lung(std::__cxx11::string&, Node*)': main.cpp:63:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < str.size(); ++i){ ~~^~~~~~~~~~~~ main.cpp:73:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i == str.size() && aux != nullptr && aux->prefix != 0){ ~~^~~~~~~~~~~~~