Compilare: main.cpp: In function 'long long int x(std::string&)': main.cpp:18:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 18 | for (int i = 1; i < a.size(); i++) { | ~~^~~~~~~~~~ main.cpp:25:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 25 | for (int i = 0; i < a.size(); i++) { | ~~^~~~~~~~~~