/in/foo.cc: In member function 'DateTime& DateTime::operator+(int)':
/in/foo.cc:120:8: error: 'class Date' has no member named 'Add'
   p->d.Add(daynum); 
        ^~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:160:20: error: 'class DateTime' has no member named 'Sub'
  int secondnum=dt1.Sub(dt2);
                    ^~~