完善ing——输入年月日输出这一年为该年的第多少天

#include <iostream>

using namespace std;
int days (int a);
int main()
{
    int year,month,day,sum;
    cout<<"请输入你要算的年月日："<<endl;
    cin>>year>>month>>day;
    if (month==1)
        sum=day;
    else if(month==2)
        sum=31+day;
    else
    {
        if((year%4==0 && year%100!=0 )||year%400==0)
            sum=days(month)+29;
        else
            sum=days(month)+28;
    }
   cout<<"你所输入你这一天为该年的第 "<<sum<<" 天"<<endl;
    return 0;
}

int days (int a)
{
    int num5;
    switch(a)
    {
    case 3:
        num5=31;break;
    case 5:
        num5=31*2+30;break;
    case 7:
        num5=31*3+30*2;break;
    case 8:
        num5=31*4+30*2;break;
    case 10:
        num5=31*5+30*3;break;
    case 12:
        num5=31*6+30*4;break;
    case 4:
        num5=31*2;break;
    case 6:
        num5=30*1+31*3;break;
    case 9:
        num5=31*4+30*3;break;
    case 11:
        num5=31*5+30*4;break;
    }
    return num5;
}