Compilare: main.cpp: In function 'void change(std::string, int, long long int*)': main.cpp:16:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 16 | for (int i=0; i<x.length(); i++) | ~^~~~~~~~~~~ main.cpp:18:24: 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 j=0; j<s.length(); j++) | ~^~~~~~~~~~~