输入年月日，计算出该日为该年的第几天

#include<iostream.h>
int leap(int year)
{
int lp;
lp=((year%4==0 && year%100!=0)|| (year%400==0))?1:0;
return lp;
}
int month_days(int year,int month)
{
int d;
switch (month)
{
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12: d=31; break;
case 2: d=leap(year)?29:28; break;
default :d=30;
}
return d;
}
int days(int year,int month,int day)
{
int i,ds=0;
for(i=1;i<month;i++)
{ ds=ds+month_days(year,i);
ds=ds+day;}
return ds;
}
void main()
{
int year,month,day,i_day;
cout<<"输入年月日:"<<endl;
cin>>year>>month>>day;
i_day=days(year,month,day);
cout<<year<<"-"<<month<<"-"<<day<<"是"<<year<<"的第"<<i_day<<"天"<<endl;
}