设计一个日期类date,包括日期的年份，月份和日号，编写一个友元函数求两个日期之间相差的天数。

#include <iostream.h>
class date
{
 int year;
 int month;
 int day;
public:
 date(int y,int m,int d)
 {
  year=y;month=m;day=d;
 }
 void disp()
 {
  cout << year << "." << month << "." << day << endl;
 }
 friend int count_day(date &d,int);
 friend int leap(int year);
 friend int subs(date d1,date d2);
};
int count_day(date &d,int flag)
{
 static int day_tab[2][12]={{31,28,31,30,31,30,31,31,30,31,30,31},{31,29,31,30,31,30,31,31,30,31,30,31}};
 int p,i,s;
 if(leap(d.year))
  p=1;
 else
  p=0;
 if(flag)
 {
  s=d.day;
  for(i=1;i<d.month;i++)
   s+=day_tab[p][i-1];
 }
 else
 {
  s=day_tab[p][d.month]-d.day;
  for (i=d.month+1;i<=12;i++)
   s+=day_tab[p][i-1];
 }
 return(s);
}
int leap(int year)
{
 if(year%4==0 && year%100!=0 || year%400==0)
  return 1;
 else
  return 0;
}
int subs(date d1,date d2)
{
 int days,day1,day2,y;
 if(d1.year<d2.year)
 {
  days=count_day(d1,0);
  for(y=d1.year+1;y<d2.year;y++)
   if(leap(y))
    days+=366L;
   else
    days+=365L;
   days+=count_day(d2,1);
 }
 else if (d1.year==d2.year)
 {
  day1=count_day(d1,1);
  day2=count_day(d2,1);
  days=day2-day1;
 }
 else
 {
  days=count_day(d2,0);
  for(y=d2.year+1;y<d1.year;y++)
   if(leap(y))
    days+=366L;
   else
    days+=365L;
   days+=count_day(d1,1);
 }
 return days;
}
void main()
{
 
 date d1(2000,1,1),d2(2005,10,1);
 int ds1=subs(d1,d2),ds2=subs(d2,d1);
 cout << "日期d1:";d1.disp();
 cout << "日期d2:";d2.disp();
 cout << "d1和d2相距" << ds1 << "天" << endl;
    cout << "d2和d1相距" << ds2 << "天" << endl;
}