根据年月日，判断已经多少天（3)

#include<stdio.h>
int main(void)
{
int year,month,days=0,day,flag,sum=0;int i=1;
scanf("%d",&year);
scanf("%d",&month);
scanf("%d",&day);
if(year%400==0)
flag=1;
else if(year%4==0&&year%100!=0)
flag=1;
else
flag=0;

for(i=1;i<month;i++)
{
	

	switch(i)
{
case 2:
{if(flag==1)
days=29;
else
days=28;
}break;
    case 4:
	case 6:
	case 9:
    case 11:days=30;break;
	case 1:
	case 3:
	case 5:
    case 7:
    case 8:
    case 10:
	case 12:days=31;break;


} 
	sum+=days;
}
sum=sum+day;
printf("%d\n",sum);
return 0;

}