foo.cc:30:41: error: ISO C++ forbids declaration of 'WeekdayOfTheFirstDay' with no type [-fpermissive]
   30 |  WeekdayOfTheFirstDay(int year,int month)
      |                                         ^
foo.cc: In function 'int WeekdayOfTheFirstDay(int, int)':
foo.cc:32:15: warning: unused variable 'a' [-Wunused-variable]
   32 |   int ddday=0,a=0;
      |               ^

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