Compilare: main.cpp: In function 'void buildZ(std::string&)': main.cpp:14:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 14 | for (int i=1;i<a.length();i++){ | ~^~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:38:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 38 | for (int i=0;i<a.size();i++){ | ~^~~~~~~~~