使用友元函數計算兩個日期之間間隔的天數。


#include<iostream.h>

class Date
{     private:
            int Year,Month,Day;
      public:
            Date(int NewY,int NewM,int NewD);
            int GetYear(){return Year;}
            int GetMonth(){return Month;}
            int GetDay(){return Day;}
            bool IsLeapYear();
            friend long AllDays(Date &a);
};
Date::Date(int NewY,int NewM,int NewD)
{     Year=Month=Day=1;
      if(NewY>0&&NewY<10000) Year=NewY;
      if(NewM>0&&NewM<12) Month=NewM;
      if(NewD>0&&NewD<32) Day=NewD;
}
bool Date::IsLeapzYear()
{     return (Year%4==0&&Year%100!=0)||(Year%400==0);}
long AllDays(Date &a)
{    long days=0;
     for(int i=1;i<a.Year;i++)
           if(i%4==0&&i%100!=0||i%400==0) days+=366;
           else days+=365;
     for(int i=1;i<a.Month;i++)
     {     if(i==1||i==3||i==5||i==7||i==8||i==10||i==12) days+=31;
           else if(i==4||i==6||i==9||i==11) days+=30;
                 else if(a.IsLeapYear()) days+=29;
                       else days+=28;
     }
     days+=a.Day;
     return days;   
}
void Distance(Date &a,Date &b)
{    long daysa=AllDays(a);
     long daysb=AllDays(b);
     long i;
     if(daysa>daysb) i=daysa-daysb;
     else i=daysb-daysa;
     cout<<a.GetYear()<<"年"<<a.getMonth()<<"月"<<a.GetDay()<<"日距離"
     <<b.GetYear()<<"年"<<b.GetMonth()<<"月"<<b.GetDay()<<"日有"<<i<<"天。"<<endl;
}
void main()
{    Date d1(2005,3,11);
     Date d2(2000,1,1);
     Distance(d1,d2);
}