/in/foo.cc: In function 'std::__cxx11::string Generate()':
/in/foo.cc:21:7: error: 'std::__cxx11::string {aka class std::__cxx11::basic_string<char>}' has no member named 'last'; did you mean 'at'?
  if(s.last()=='=')s=s+ch2[(g()%3+2)%4];
       ^~~~