/in/foo.cc: In member function 'int Date::difference(Date&)':
/in/foo.cc:34:37: error: no matching function for call to 'Date::YearDay()'
   34 |                         num+=YearDay();
      |                              ~~~~~~~^~
/in/foo.cc:21:13: note: candidate: 'int Date::YearDay(int)'
   21 |         int YearDay(int y){
      |             ^~~~~~~
/in/foo.cc:21:13: note:   candidate expects 1 argument, 0 provided