这段C++代码从书上拼起来的怎么不对

C/C++ code

#include<iostream>
using namespace std;

#ifndef DATE_H
#define DATE_H
class Date
{
public:
    Date(int newYear, int newMonth, int newDay);
    int getYear();
    void setYear(int newYear);

private:
    int year;
    int month;
    int day;
};
#endif


Date::Date(int newYear, int newMonth, int newDay)
{
    year=newYear;//this->year=newYear;
    month=newMonth;//this->month=newMonth;
    day=newDay;//this->day=newDay;
}

int Date::getYear()
{
    return year;
}

void Date::setYear(int newYear)
{
    year=newYear;//this->year=newYear;

};

class Person
{
    Person(int id, int year, int month ,int day);
    int getId();
    Date *getBirthDate();

private:
    int id;
    Date * birthDate;
};


Person::Person(int id, int year,int month, int day)
{
    this->id=id;
    birthDate=new Date(year, month, day);
}

int Person::getId()
{
    return id;
}

Date* Person::getBirthDate()
{
    return birthDate;
};


int main()
{
    Person person(11112,1992,5,29);
    cout<<"birth year before the change is "
        <<person.getBirthDate()->getYear()<<endl;
    Date *pDate=person.getBirthDate();
    pDate->setYear (2011);
    cout<<"birth yera after the change is"<<person.getBirthDate()->getYear()<<endl;


    system("PAUSE");
    return 0;
}

另外 year month day是private里面的为什么可以 year=newyear; 不一定用year->newyear;

什么意思？

你的person类中应该有声明public，如果没有的话，默认是private.改正如下：
class Person
{
public:
  Person(int id, int year, int month ,int day);
  int getId();
  Date *getBirthDate();

private:
  int id;
  Date * birthDate;
};

person类都没有public的方法了，当然不行了。