求某一日期是当年的第几天？

//---------------------------------------------------------------------------

#include <stdio.h>

int iy(int year)
{
return (year%4==0&&year%100||year%400==0)?1:0;
}
int main(int argc, char* argv[])
{
int y,m,d,i,yd;
scanf("%d %d %d",&y,&m,&d);/*输出年、月、日，用空格分隔*/
yd=d;
if (m>1)
for (i=1; i<m; i++)
switch (i) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:yd+=31;break;
case 4:
case 6:
case 9:
case 11:yd+=30;break;
case 2:yd+=iy(y)?29:28;break;
}

printf("%d\n",yd);/*输出结果*/
return 0;
}
//---------------------------------------------------------------------------

int Days(int y,int m,int d)/*分别是年月日*/
{
int dd[]={31,28,31,30,31,30,31,31,30,31,30,31};/*所有月份的天数*/
int i,s=0;
if((y%