C++ class Date

<pre name="code" class="cpp">#include<iostream>#include<windows.h>using namespace std;static int data[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};class Date{    friend int count(const Date &);//有元函数，计算该日期是该年的第几天    friend bool leap_year(int);//判断是否为闰年    friend bool operator<(Date &,Date &);//重载<    friend bool operator>(Date &,Date &);//重载>    friend bool operator==(Date &,Date &);//重载==public:    Date();//默认构造函数    void set(int,int,int);//设置日期    Date& operator-(int);//一个日期减去天数    Date& operator+(int);//一个日期加上天数    int sum();//从0天开始算起，该日期一共多少天    void display();//显示日期private:    int year,month,day;//定义私有变量};Date::Date(){    year=month=day=0;}bool leap_year(int y){    if(y%400==0||(y%4==0&&y%100!=0))    {        data[2]=29;        return true;    }    return false;}void Date::set(int y,int m,int d){    year=y>0?y:0;    month=(m>0&&m<=12)?m:0;    leap_year(y);    day=(d>0&&d<=data[m])?d:0;}int Date::sum(){    int sum;    if(leap_year(year))       sum=(year-1)*366;    sum=(year-1)*365;    for(int i=1;i<month;i++)       sum+=data[i];    sum+=day;    return sum;}int count(const Date &a){    int count=0;    leap_year(a.year);    for(int i=0;i<a.month;i++)      count+=data[i];    count+=a.day;    return count;}bool operator<(Date &a,Date &b){    return a.sum()<b.sum();}bool operator>(Date &a,Date &b){    return a.sum()>b.sum();}bool operator==(Date &a,Date &b){    return a.sum()==b.sum();}Date& Date::operator+(int x){    int flag=0;    if(x==0)      return *this;    leap_year(year);    if((day+x)>data[month])    {        month++;        flag++;        if(month>12)        {            year++;            month=1;        }    }    if(flag==0)       day+=x;    else       day=x;    return *this;}Date& Date::operator-(int x){    int flag=0;    if(x==0)      return *this;    leap_year(year);    if(day<=x)    {        month--;        flag++;        if(month<1)        {            year--;            month=12;        }    }    if(flag==0)      day-=x;    day=data[month]+1-x;    return *this;}int operator-(Date &a,Date &b){    int t;    if(a==b)      t=a.sum()-b.sum();    else if(a<b)      t=b.sum()-a.sum();    else      t=a.sum()-b.sum();}void Date::display(){    cout<<year<<"年"<<month<<"月"<<day<<"日"<<endl;}int main(){    Date a,b;    cout<<"set date"<<endl;    a.set(2000,2,29);    b.set(2000,2,1);    cout<<"data a:"<<endl;    a.display();    cout<<"data b:"<<endl;    b.display();    cout<<"从0开始该日期共多少天"<<endl;    cout<<count(a);    cout<<endl;    cout<<"date a>date b"<<endl;    cout<<(a>b)<<endl;    cout<<"date a<date b"<<endl;    cout<<(a<b)<<endl;    cout<<"date a==date b"<<endl;    cout<<(a==b);}

结果如下：