第十二周项目1-求某年某月是本年的第几天

#include <iostream>
using namespace std;
int time(int,int,int);
int main( )
{
int year,month,day,z;
cout<<"请依次输入年、月、日:"<<endl;
cin>>year>>month>>day;
z=time(year,month,day);
cout<<year<<"年"<<month<<"月"<<day<<"日是第"<<z<<"天"<<endl;
return 0;
}
int time(int year,int month,int day)
{
int z,a;
if(year%4==0&&year%100!=0||year%400==0)
{
a=29;

}else
a=28;
switch(month)
{
case 1:z=day;break;
case 2:z=31+day;break;
case 3:z=31+a+day;break;
case 4:z=31*2+a+day;break;
case 5:z=2*31+30+a+day;break;
case 6:z=3*31+30+a+day;break;
case 7:z=31*3+30*2+a+day;break;
case 8:z=31*4+30*2+a+day;break;
case 9:z=31*5+30*2+a+day;break;
case 10:z=5*31+30*3+a+day;break;
case 11:z=6*31+30*3+a+day;break;
case 12:z=6*31+30*4+a+day;break;
}

return z;
}