Question

一个C++简单程序的问题

题目是：先建立一个Point(点)类，包含数据成员x，y(坐标点)。以它为基类，派生出一个Circle(圆)类，增加数据成员r(半径)，再以Circle类为直接基类，派生出一个Cylinder(圆柱体)类，再增加数据成员h(高)。要求编写程序，重载运算符“<<” 和“>>”，使之能用于输出以上类对象。

我写的程序：
#include<iostream.h>
#include<stdlib.h>
class Point
{
private:
int x;
int y;
public:
Point(int x,int y)
{
this->x=x;
this->y=y;
}
int getX()
{
return x;
}
int getY()
{
return y;
}
~Point()
{}
};

class Circle: public Point
{
private:
float r;
public:
Circle(int x,int y,float r)
:Point(x,y)
{
this->r=r;
}
float getR()
{
return r;
}
~Circle()
{}
};

class Cylinder:public Circle
{
private:
float h;
public:
Cylinder(int x,int y,float r,float h)
:Circle(x,y,r)
{
this->h=h;
}
float getH()
{
return h;
}
friend istream & operator >> (istream &in, Cylinder &c1);
friend ostream & operator << (ostream &out, Cylinder &c1);
};

istream & operator>>(istream &in,Cylinder &c1)
{
cout<<"请输入坐标:\n";
in>>c1.x>>c1.y;
cout<<"请输入半径:\n";
in>>c1.r;
cout<<"请输入高:\n";
in>>c1.h;
return in;
}

ostream & operator << (ostream &out,Cylinder &c1)
{
out<<"坐标为"<<"("<<c1.getX()<<","<<c1.getY()<<")"<<endl;
out<<"半径为"<<c1.getR()<<endl;
out<<"高为"<<c1.getH()<<endl;
return out;
}

int main()
{
Cylinder a;
cin>>a;
cout<<a;
return 0;
}

但是编译器报错：:\Backup\我的文档\C++程序\3\3.cpp(65) : error C2248: 'x' : cannot access private member declared in class 'Point'
D:\Backup\我的文档\C++程序\3\3.cpp(6) : see declaration of 'x'
D:\Backup\我的文档\C++程序\3\3.cpp(65) : error C2248: 'y' : cannot access private member declared in class 'Point'
D:\Backup\我的文档\C++程序\3\3.cpp(7) : see declaration of 'y'
D:\Backup\我的文档\C++程序\3\3.cpp(67) : error C2248: 'r' : cannot access private member declared in class 'Circle'
D:\Backup\我的文档\C++程序\3\3.cpp(29) : see declaration of 'r'
D:\Backup\我的文档\C++程序\3\3.cpp(85) : error C2512: 'Cylinder' : no appropriate default constructor available
执行 cl.exe 时出错.

哪位大侠可以帮俺改改啊~~让它可以运行~~~

Answer 1

#include<iostream.h>
#include<stdlib.h>
class Point
{
private:
int x;
int y;
public:
Point(int x,int y)
{
this->x=x;
this->y=y;
}
void setX(int a)
{
x=a;
}
void setY(int a)
{
y=a;
}
int getX()
{
return x;
}
int getY()
{
return y;
}
~Point()
{}

};

class Circle: public Point
{
private:
float r;
public:
Circle(int x,int y,float r)
:Point(x,y)
{
this->r=r;
}
void setR(float a)
{
r=a;
}
float getR()
{
return r;
}
~Circle()
{}
};

class Cylinder:public Circle
{
private:
float h;
public:
Cylinder():Circle(0,0,0),h(0){}
Cylinder(int x,int y,float r,float h)
:Circle(x,y,r)
{
this->h=h;
}
void setH(float a)
{
h=a;
}
float getH()
{
return h;
}
friend istream & operator >> (istream &in, Cylinder &c1);
friend ostream & operator << (ostream &out, Cylinder &c1);
};

istream & operator>>(istream &in,Cylinder &c1)
{
int _x,_y;
float _h,_r;

cout<<"请输入坐标:\n";
in>>_x>>_y;
cout<<"请输入半径:\n";
in>>_r;
cout<<"请输入高:\n";
in>>_h;
c1.setX(_x);
c1.setY(_y);
c1.setR(_r);
c1.setH(_h);
return in;
}

ostream & operator << (ostream &out,Cylinder &c1)
{
out<<"坐标为"<<"("<<c1.getX()<<","<<c1.getY()<<")"<<endl;
out<<"半径为"<<c1.getR()<<endl;
out<<"高为"<<c1.getH()<<endl;
return out;
}

int main()
{
Cylinder a;
cin>>a;
cout<<a;
return 0;
}

楼上的都说错了！ 即使的getX（） 也只是返回的一个拷贝！ 仅仅返回的是一个值！不能改变原来对象的field!应该写一个set 函数！ 值传递的知识 楼上的根本就不懂啊！ 汗！

Answer 2

#include<iostream>
#include<stdlib.h>
using namespace std;
class Point
{
protected: //改成保护成员
int x;
int y;
public:
Point(){} //添加默认构造函数
Point(int x,int y)
{
this->x=x;
this->y=y;
}
int getX()
{
return x;
}
int getY()
{
return y;
}
~Point()
{}
};

class Circle: public Point
{
protected: //改成保护成员
float r;
public:
Circle(){} //添加默认构造函数
Circle(int x,int y,float r)
:Point(x,y)
{
this->r=r;
}
float getR()
{
return r;
}
~Circle()
{}
};

class Cylinder:public Circle
{
private: //改成保护成员
float h;
public:
Cylinder() //添加默认构造函数
{}
Cylinder(int x,int y,float r,float h)
:Circle(x,y,r)
{
this->h=h;
}
float getH()
{
return h;
}
friend istream & operator >> (istream &in, Cylinder &c1);
friend ostream & operator << (ostream &out, Cylinder &c1);
~Cylinder() //添加析构函数
{}
};

istream & operator>>(istream &in,Cylinder &c1)
{
cout<<"请输入坐标:\n";
in>>c1.x>>c1.y;
cout<<"请输入半径:\n";
in>>c1.r;
cout<<"请输入高:\n";
in>>c1.h;
return in;
}

ostream & operator << (ostream &out,Cylinder &c1)
{
out<<"坐标为"<<"("<<c1.getX()<<","<<c1.getY()<<")"<<endl;
out<<"半径为"<<c1.getR()<<endl;
out<<"高为"<<c1.getH()<<endl;
return out;
}

int main()
{
Cylinder a;
cin>>a;
cout<<a;
return 0;
}
ps.1.创建对象时，要调用构造函数，当你自己创建了一个构造函数后，程序便不再自动生成默认构造函数，所以你要自己加上（无参数）；
2.每个类都要有析构函数；
3.公有继承的派生类，不能访问基函数的私有成员。

Answer 3

private:
int x;
int y;
你定义了，x,y是私用的，当然不能直接用了，所以，编译时候，会报错.
若要用到x,y的值，你可以用下面2个函数，这也是为什么要定义这2个函数的原因
int getX()
{
return x;
}
int getY()
{
return y;
}
这2个函数的返回值都是int ,你可以把它的返回值赋给你要用的变量.

这个程序，好像在哪里的书上看过.....认真对比下书，就懂了。

Answer 4

你那个x,y是private的,不能直接c1.x

写个getx()