Compilare: main.cpp: In function 'bool ok(int)': main.cpp:21:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 21 | for(int i=0;i<b.size();++i) | ~^~~~~~~~~ main.cpp:29:13: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 29 | if(i==b.size()-1) | ~^~~~~~~~~~~~