计算第几天，无语了

#include<iostream>
using namespace std;
struct Date
{
    int year;
    int month;
    int day;
};
int main()
{
    Date date;
    cout<<"input year,month,day:";
    cin>>date.year>>date.month>>date.day;
    int days=0;
    int i;
    if(date.month==1)
        days=days+date.day;
    else
        for(i=1;i<date.month;i++)
    {
         if(i==1||i==3||i==5||i==7||i==8||i==10||i==12)
            days=days+31;
        else if(i==4||i==6||i==9||i==11)
            days=days+30;
            else if(i==2)
                days=days+29;
    }days=days+date.day;
if(date.month>=3&&(date.year%4!=0||date.year%400!=0))
    days=days-1;
    cout<<date.month<<"月"<<date.day<<"日是"<<date.year<<"年的第"<<days<<"天."<<endl;
    return 0;
}