foo.cc: In member function 'void Date::add(int)':
foo.cc:35:3: error: 'mont2h' was not declared in this scope
   mont2h=day/a[month-1]+month;
   ^~~~~~
foo.cc:35:3: note: suggested alternative: 'month'
   mont2h=day/a[month-1]+month;
   ^~~~~~
   month

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。