/in/foo.cc: In function 'void change(std::__cxx11::string)':
/in/foo.cc:16:6: error: 'size_type' was not declared in this scope
  for(size_type i=0;i!=in.size();++i){
      ^~~~~~~~~
/in/foo.cc:16:20: error: 'i' was not declared in this scope
  for(size_type i=0;i!=in.size();++i){
                    ^