Compilare: main.cpp: In function 'int main()': main.cpp:18:22: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 18 | for(int i = 0; i < a.size(); ++i) | ~~^~~~~~~~~~