计算该日是本年的第几天

#include <stdio.h>
struct y_m_d
{
int year;
int month;
int day;
};

int days(struct y_m_d date)
{   int sum=0,i;
int a[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};//每个元素用逗号隔开
for(i=0;i<date.month;i++)//结构体成员前面不能加上取值符号
sum+=a[i];
sum+=date.day;
if(date.month>2&&((date.year%4==0&&date.year%100!=0)||date.year%400==0))
sum++;
return sum;

}

int main()
{
struct y_m_d date;//加上结构体符号
int days(struct y_m_d date);//括号中加入结构体
int day_sum;
scanf("%d%d%d",&date.year,&date.month,&date.day);
day_sum=days(date);
printf("%d\n",day_sum);
return 0;
}