用结构体计算一天在一年中的天数

#include "stdafx.h"
#include"iostream"
using namespace std;
struct Date
{
int year;
int month;
int day;
};
int main()
{
int sum;
sum=0;
struct Date date;
int a[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
cin>>date.year;
cin>>date.month;
cin>>date.day;
if(date.year%4==0&&date.year%100!=0 || date.year%400==0)
{
if(date.month>2)
date.day=date.day+1;
else
date.day=date.day ;
for(int i=1;i<date.month;i++)
{sum=sum+a[i];}
sum=sum+date.day;
cout<<sum<<endl;

}
else
{
date.day=date.day;
for(int i=1;i<date.month;i++)
{sum=sum+a[i];}
sum=sum+date.day;
cout<<"";
cout<<sum<<endl;
}
return 0;
}