foo.cc: In function 'int IsLeapYear(int)':
foo.cc:35:27: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  if(year%400==0||year%4==0&&year%100!=0)
                  ~~~~~~~~~^~~~~~~~~~~~~
foo.cc: In function 'int WeekdayOfTheFirstDay(int, int)':
foo.cc:25:7: warning: 'days' may be used uninitialized in this function [-Wmaybe-uninitialized]
   days+=DaysOfYear(y);
   ~~~~^~~~~~~~~~~~~~~

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