Compilare: main.cpp: In function 'void add(std::string)': main.cpp:26:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 26 | for(int i=0; i<s.length(); i++){ | ~^~~~~~~~~~~ main.cpp: In function 'void del(std::string)': main.cpp:41:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 41 | for(int i=0; i<s.length(); i++){ | ~^~~~~~~~~~~ main.cpp: In function 'int app(std::string)': main.cpp:52:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 52 | for(int i=0; i<s.length(); i++){ | ~^~~~~~~~~~~ main.cpp: In function 'int pref(std::string)': main.cpp:73:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 73 | for(int i=0; i<s.length(); i++){ | ~^~~~~~~~~~~