设计一个日期类Date，包括年、月、日等私有数据成员。要求实现日期的基本运算，如一日期加上天数、一日期

这个我做过，你照着改吧，函数名字跟你的不一样
#ifndef HEADER_DATE
#define HEADER_DATE
#include
#include
#include
using namespace std;

class date{
int year,month,day;
void init();
public:
static const int tians[];
int age();
int getyear(){return year;}
int getmonth(){return month;}
int getday(){return day;}
date();
date(const string& s);
date(const date& d){year=d.year,month=d.month,day=d.day;}
date(int y=2000,int m=1,int d=1);
bool isleapyear()const;
friend ostream& operator<<(ostream& o,const date& d);
double xg();
double xiangge(date b);
friend date operator+=(date& a,int n);
friend bool operator==(date& a,date & b);
void display();
string huanyuan();
};

#endif
#include"date.h"

//日期的计算
const int date::tians[]={0,31,59,89,120,150,181,212,242,273,303,334};
const long int year4=1461;
const long int year100=36524;
const long int year400=146097;
using namespace std;

void date::init(){
if(year>5000||month>12||day>31||day<1||month<1||year<1)
{cout<<"年月日范围出错！"<exit(1);
}
}
date::date(int y,int m, int d):year(y),month(m),day(d){

init();
}
date::date(const string& s):da(s){
year=atoi(s.substr(0,4).c_str());
month=atoi(s.substr(5,2).c_str());
day=atoi(s.substr(8,2).c_str());
}
bool date::isleapyear()const{
if(year%4==0&& year%100!=0 ||year%400==0)
return true;
return false;
}
ostream& operator<<(ostream& o,const date& d){
o<return o;
}
date operator+=(date& a,int n){
switch(a.month){
case 4:
case 6:
case 9:
case 11:{if((a.day+n)>30){a.month+=(a.day+n)/30;a.day=(a.day+n+1)%30;}else a.day+=n;if(a.month>12){a.year+=a.month/12;a.month%=12;} break;}
case 2:
{if(a.day>29){cout<<"错误,日期 超出范围"<if((a.year%4==0 && a.year%100!=0 )||a.year%400==0)
{if(a.day+n>29){a.month+=(a.day+n)/29;a.day=(a.day+n+1)%29;} else a.day+=n;if(a.month>12){a.year+=a.month/12;a.month%=12;}break;}
else {
if(a.day+n>28){a.month+=(a.day+n)/28;a.day=(a.day+n+1)%28;}else a.day+=n;if(a.month>12){a.year+=a.month/12;a.month%=12;}}break;
}
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:{if(a.day+n>31){a.month+=(a.day+n)/31;a.day=(a.day+n)%31;}else a.day+=n; if(a.month>12){a.year+=a.month/12;a.month%=12;}}break; }
return a;
}

double date::xg(){
int days1[12]={0,31,59,90,120,151,181,212,243,273,304,334};
long int sum1; //4年一共1461天
sum1=year/400*year400+year%400/100*year100+year%400%100/4*year4+year%400%100%4*365; //年份转换为天数所得
for(int i=0;i<12;i++)
if(month-1==i) sum1+=days1[i]+day;
return sum1;
}
double date::xiangge(date b){
return (xg()-b.xg());
}
bool operator==(date& a,date & b){
if(a.year==b.year && a.month==b.month&& a.day==b.day) return 1;
else return 0;
}
void date::display(){
cout<}
date::date(){ //无参为系统时间
time_t timer;
struct tm* t_tm;
time(&timer);
t_tm=localtime(&timer);
year=t_tm->tm_year+1900,
month=t_tm->tm_mon+1,
day=t_tm->tm_mday;
}
int date::age(){ //计算当前时间差
time_t timer;
struct tm* t_tm;
time(&timer);
t_tm=localtime(&timer);
int y=t_tm->tm_year+1900,
m=t_tm->tm_mon+1,
d=t_tm->tm_mday;
if(m else return (y-year);
}
string date::huanyuan(){
string m; char a1[10],b1[10], c1[10];
itoa(year, a1, 10);
itoa(month,b1, 10);
itoa(day, c1, 10);
m+=a1;
m+='/';
m+=b1;
m+='/';
m+=c1;
return m;
}

这很简答，但也不是一言两语说得清的.......
class CDate
{
private:
int m_Year;
int m_Month;
int m_Day;
// 添加 你自己的 成员变量
public:
CDate();
~CDate();
void DayAdd(int day);
void MonthAdd(int month);
void YearAdd(int year);
// 添加你自己的 成员函数
};