foo.cc: In function 'int passDays(int, int, int)':
foo.cc:35:9: warning: 'sum' may be used uninitialized in this function [-Wmaybe-uninitialized]
   35 |  return sum;
      |         ^~~
foo.cc: In function 'int WeekdayOfTheFirstDay(int, int)':
foo.cc:50:7: warning: 'sum' may be used uninitialized in this function [-Wmaybe-uninitialized]
   50 |  days += passDays(year, month, 1);
      |  ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务