自己定义三个类即点、线和矩形，通过带参数的构造函数完成对对象的初始化赋值，三个类中都要实现一个显示的操作，要求该操作能够完成显示点和线（两个端点）的坐标数值。线的类中除了显示的操作外还要有一个显示线段长度的操作。矩形的类中除了显示的操作外还要有一个显示矩形面积的操作。

类是这样的：
point ：  Private:x,y    public:void draw()

line：Private:point p1,p2  public:void draw()  Distance()

rect：Private:point u1,u2  public:void draw()  Area()

主函数是这样的：
#include <iostream>
using namespace std;

void main()
{
    point p(2,3);
    point p11(3,8),
        p21(7,5);
    line l(p11,p21);
    rect r(p11,p21);
    p.draw();
    l.draw();
    r.draw();
    cout<<"线的长度为："<<l.Distance()<<endl;
    cout<<"矩形的面积为："<<r.Area()<<endl;
}
输出之后是这样的：
point的x坐标值是：2  point的y坐标值是：3
line的起点是point的x坐标值是：3  point的y坐标只是：8
line的终点为point的x坐标值是：7  point的y坐标值是：5
rect的起点为point的x坐标值是：3  point的y坐标值是：8
rect的重点为point的x坐标值是：7  point的y坐标值是：5
线的长度为：5
矩形的面积为：12


请大家帮帮忙，把这个程序补充完整，谢谢，今晚就要

这是我写的！希望对你有用！

#include <iostream>
#include <cmath>
using namespace std;
class point
{
public:
    double x;
    double y;
    point(double x1=0,double y1=0):x(x1),y(y1)
    {}
    void draw()
    {
        cout<<"point的x坐标值是:"<<x<<"   point的y坐标值是："<<y<<endl;
    }
};
class line:public point
{
private:
    point p1;
    point p2;
public:
    line(point xp1,point xp2):p1(xp1.x,xp1.y),p2(xp2.x,xp2.y)
    {}
    void draw()
    {
        cout<<"line的起点是point的x坐标值是："<<p1.x<<"   point的y坐标值是:"<<p1.y<<endl;
        cout<<"line的终点为point的x坐标值是："<<p2.x<<"   point的y坐标值是:"<<p2.y<<endl;
    }
    double Distance()
    {
        double m=(p2.x-p1.x)*(p2.x-p1.x)+(p2.y-p1.y)*(p2.y-p1.y);
        return sqrt(m);
    }
};
class rect :public point
{
private:
    point u1;
    point u2;
public:
    rect(point ru1,point ru2):u1(ru1.x,ru1.y),u2(ru2.x,ru2.y)
    {}
    void draw()
    {
        cout<<"rect的起点为point的x坐标值是:"<<u1.x<<"  point的y坐标值是："<<u1.y<<endl;
        cout<<"rect的终点为point的x坐标值是："<<u2.x<<" point的y坐标值是："<<u2.y<<endl;
    }
    double Area()
    {
        return fabs((u2.x-u1.x)*(u2.y-u1.y));
    }
};

int  main()
{
    point p(2,3);
    point p11(3,8);
    point p21(7,5);
    line l(p11,p21);
    rect r(p11,p21);
    p.draw();
    l.draw();
    r.draw();
    cout<<"线的长度为："<<l.Distance()<<endl;
    cout<<"矩形的面积为："<<r.Area()<<endl;
}

谢谢，但是类图中的x与y是私有的，你变成是公有的了，这是不允许更改的。

那你就声明友元类啊！如下：

#include <iostream>
#include <cmath>
using namespace std;
class point
{
private:
    double x;
    double y;
public:
    point(double x1=0,double y1=0):x(x1),y(y1)
    {}
    void draw()
    {
        cout<<"point的x坐标值是:"<<x<<"   point的y坐标值是："<<y<<endl;
    }
    friend class line;
    friend class rect;
};
class line
{
private:
    point p1;
    point p2;
public:
    line(point xp1,point xp2):p1(xp1.x,xp1.y),p2(xp2.x,xp2.y)
    {}
    void draw()
    {
        cout<<"line的起点是point的x坐标值是："<<p1.x<<"   point的y坐标值是:"<<p1.y<<endl;
        cout<<"line的终点为point的x坐标值是："<<p2.x<<"   point的y坐标值是:"<<p2.y<<endl;
    }
    double Distance()
    {
        double m=(p2.x-p1.x)*(p2.x-p1.x)+(p2.y-p1.y)*(p2.y-p1.y);
        return sqrt(m);
    }
};
class rect
{
private:
    point u1;
    point u2;
public:
    rect(point ru1,point ru2):u1(ru1.x,ru1.y),u2(ru2.x,ru2.y)
    {}
    void draw()
    {
        cout<<"rect的起点为point的x坐标值是:"<<u1.x<<"  point的y坐标值是："<<u1.y<<endl;
        cout<<"rect的终点为point的x坐标值是："<<u2.x<<" point的y坐标值是："<<u2.y<<endl;
    }
    double Area()
    {
        return fabs((u2.x-u1.x)*(u2.y-u1.y));
    }
};

int  main()
{
    point p(2,3);
    point p11(3,8);
    point p21(7,5);
    line l(p11,p21);
    rect r(p11,p21);
    p.draw();
    l.draw();
    r.draw();
    cout<<"线的长度为："<<l.Distance()<<endl;
    cout<<"矩形的面积为："<<r.Area()<<endl;
}

class point
{
    double x;
    double y;
public:
    point(double x1=0,double y1=0):x(x1),y(y1)
    {}
    double get_x(){ return x;}
    double get_y(){ return y;}
    void draw()
    {
        cout<<"point的x坐标值是:"<<x<<"   point的y坐标值是："<<y<<endl;
    }
};

d:\msdev98\myprojects\c++\kao\point.h(3) : error C2011: 'point' : 'class' type redefinition

这个错误说明了什么啊，我的程序中有头文件，和源文件

// 重定义错误
#include <iostream>
#include <cmath>
using namespace std;
class point
{
    double x;
    double y;
public:
    point(double x1=0,double y1=0):x(x1),y(y1)
    {}
    double get_x(){ return x;}
    double get_y(){ return y;}
    void draw()
    {
        cout<<"point的x坐标值是:"<<x<<"   point的y坐标值是："<<y<<endl;
    }
};

class line:public point
{
private:
    point p1;
    point p2;
public:
    line(point xp1,point xp2):p1(xp1.get_x(),xp1.get_y()),p2(xp2.get_x(),xp2.get_y())
    {}
    void draw()
    {
        cout<<"line的起点是point的x坐标值是："<<p1.get_x()<<"   point的y坐标值是:"<<p1.get_y()<<endl;
        cout<<"line的终点为point的x坐标值是："<<p2.get_x()<<"   point的y坐标值是:"<<p2.get_y()<<endl;
    }
    double Distance()
    {
        double m=(p2.get_x()-p1.get_x())*(p2.get_x()-p1.get_x())+(p2.get_y()-p1.get_y())*
            (p2.get_y()-p1.get_y());
        return sqrt(m);
    }
};
class rect :public point
{
private:
    point u1;
    point u2;
public:
    rect(point ru1,point ru2):u1(ru1.get_x(),ru1.get_y()),u2(ru2.get_x(),ru2.get_y())
    {}
    void draw()
    {
        cout<<"rect的起点为point的x坐标值是:"<<u1.get_x()<<"  point的y坐标值是："<<u1.get_y()<<endl;
        cout<<"rect的终点为point的x坐标值是："<<u2.get_x()<<" point的y坐标值是："<<u2.get_y()<<endl;
    }
    double Area()
    {
        return fabs((u2.get_x()-u1.get_x())*(u2.get_y()-u1.get_y()));
    }
};

int  main()
{
    point p(2,3);
    point p11(3,8);
    point p21(7,5);
    line l(p11,p21);
    rect r(p11,p21);
    p.draw();
    l.draw();
    r.draw();
    cout<<"线的长度为："<<l.Distance()<<endl;
    cout<<"矩形的面积为："<<r.Area()<<endl;
    return 0;
}

'point' : no appropriate default constructor available
这个问题应该怎么解决呢，我建立了头文件和源文件，不是在一个文件下编写的

在一个文件下运行的程序我做完了，我想寻求一个在多个头文件与源文件下运行这个程序的代码，希望能帮我解决一下，谢谢

给个例子你参考下
//c.h文件
#ifndef c_h
#define c_h
class point
{
    double x;
    double y;
public:
    point(double x1=0,double y1=0);
    double get_x();
    double get_y();
    void draw();
};

class line:public point
{
private:
    point p1;
    point p2;
public:
    line(point xp1,point xp2);
    void draw();
    double Distance();
};

class rect :public point
{
private:
    point u1;
    point u2;
public:
    rect(point ru1,point ru2);
    void draw();
    double Area();
};
#endif
////////////////////////////////
//work.cpp文件
#include <iostream>
#include <cmath>
#include "c.h"
using namespace std;

point::point(double x1,double y1):x(x1),y(y1)
{}
   
double point::get_x()
{ return x;}

double point::get_y()
{ return y;}

void point::draw()
{
    cout<<"point的x坐标值是:"<<x<<"   point的y坐标值是："<<y<<endl;
}

line::line(point xp1,point xp2):p1(xp1.get_x(),xp1.get_y()),p2(xp2.get_x(),xp2.get_y())
{}
void line::draw()
{
    cout<<"line的起点是point的x坐标值是："<<p1.get_x()<<"   point的y坐标值是:"<<p1.get_y()<<endl;
    cout<<"line的终点为point的x坐标值是："<<p2.get_x()<<"   point的y坐标值是:"<<p2.get_y()<<endl;
}

double line::Distance()
{
    double m=(p2.get_x()-p1.get_x())*(p2.get_x()-p1.get_x())+(p2.get_y()-p1.get_y())*
        (p2.get_y()-p1.get_y());
    return sqrt(m);   
}

rect::rect(point ru1,point ru2):u1(ru1.get_x(),ru1.get_y()),u2(ru2.get_x(),ru2.get_y())
{}

void rect::draw()
{
    cout<<"rect的起点为point的x坐标值是:"<<u1.get_x()<<"  point的y坐标值是："<<u1.get_y()<<endl;
    cout<<"rect的终点为point的x坐标值是："<<u2.get_x()<<" point的y坐标值是："<<u2.get_y()<<endl;
}

double rect::Area()
{
        return fabs((u2.get_x()-u1.get_x())*(u2.get_y()-u1.get_y()));
}
//////////////////////////
//main.cpp文件
#include "c.h"
#include <iostream>
using namespace std;

int  main()
{
    point p(2,3);
    point p11(3,8);
    point p21(7,5);
    line l(p11,p21);
    rect r(p11,p21);
    p.draw();
    l.draw();
    r.draw();
    cout<<"线的长度为："<<l.Distance()<<endl;
    cout<<"矩形的面积为："<<r.Area()<<endl;
    return 0;
}