/in/foo.cc: In member function 'void Data::change(std::__cxx11::string)':
/in/foo.cc:28:11: warning: statement has no effect [-Wunused-value]
   for (len; len > 8; len -= 8)
           ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:56:6: warning: unused variable 'ka' [-Wunused-variable]
  int ka = 0, kb = 0, i;
      ^~
/in/foo.cc:56:14: warning: unused variable 'kb' [-Wunused-variable]
  int ka = 0, kb = 0, i;
              ^~
/in/foo.cc:62:30: warning: iteration 49 invokes undefined behavior [-Waggressive-loop-optimizations]
   a.u[i] += b.u[i], a.u[i+1] += a.u[i] / INF, a.u[i] %= INF;
                     ~~~~~~~~~^~~~~~~~~~~~~~~
/in/foo.cc:60:16: note: within this loop
  for (i = 0; i < 50; i++)
              ~~^~~~