编程一个日历出问题了

大佬能不能看一下这个哪里出问题了。

#include<stdio.h>
int main() {
  int days[12]={31,28,31,30,31,30,31,31,30,31,30,31};
  int i, year, month, day, a;
  scanf("%d %d %d", &year,&month,&day);
  if((year%4==0&&year%100!=0)||year%400==0) days[1]=29;
  for(a=day, i=0; i<month-1; i++){
    a += days[i];
  }

   printf("%d\n", a);
    
}