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:40:22: 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:49:22: 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:64:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < str.size(); ++i){ ~~^~~~~~~~~~~~