C++6.0 习题: 输入某年某月某日,判断这一天是这一年的第几天,怎么做哎!

#include<stdio.h>
void main()
{
int year,month,day,riz;
printf("现在是公园多少年?");
scanf("%d",&year);
printf("现在是几月?");
scanf("%d",&month);
printf("今天是几号?");
scanf("%d",&day);
if(( year % 4 == 0 && year % 100 != 0)||(year%400==0))
{
switch(month)
{
case 1:
riz = day;
printf("今天是今年的第%d天",riz);
break;
case 2:
riz = 31 + day;
printf("今天是今年的第%d天",riz);
break;
case 3:
riz = 31 +29 +day;
printf("今天是今年的第%d天",riz);
break;
case 4:
riz = 31 + 29 +31 +day;
printf("今天是今年的第%d天",riz);
break;
case 5:
riz = 31 + 29 + 31 + 30 + day;
printf("今天是今年的第%d天",riz);
break;
case 6:
riz = 31 +29 + 31 +30 +31 + day;