根据年月日，判断已经多少天（4)

#include<stdio.h>
int main(void)
{
	int year,month,days=0,day,flag,sum=0;
    printf("Please input year:");          
	scanf("%d",&year);                    
	printf("Please input month:");          
	scanf("%d",&month);
	printf("Please input day:");   
    scanf("%d",&day);
	if(year%400==0)
		flag=1;
	else if(year%4==0&&year%100!=0)
		flag=1;
	else flag=0;
	switch(month-1)
	{
	case 11: days+=30;
	case 10: days+=31;
	case 9: days+=30;
	case 8: days+=31;
	case 7: days+=31;
	case 6: days+=30;
	case 5: days+=31;
	case 4: days+=30;
	case 3: days+=31;
	case 2:
		{
			if(flag==1)
				days+=29;
			else days+=28;
		}
	case 1:days+=31;
	case 0:break;
	}
	sum=days+day;
	printf("%d",sum);
}