.. _ch12-xt1:

习题1
=======

| 题目要求对例题12.1进行修改，将类的定义写到头文件（后缀为.h），类的成员函数声明部分写到源文件（后缀为.cpp）。
| 所以先打开396页看这道例题

**一般每次的开头都先写的，现在只在main.cpp里写，其他的文件不用写上。**

.. code-block:: c++

   #include <iostream>
   using namespace std;

因为最后其他的文件都得要包含到main函数所在的main.cpp文件里的。

**相当于把以前每一个类的声明，类外成员函数的定义都独立剪切到一个文件里。**

每个派生类都包含它所继承的类，最后在main.cpp文件里只需包含最终的派生类就可以了。

Ponit类
--------

声明Point类
``````````````

新建point.h 头文件


.. code-block:: c++ 

   class Point   //它是基类，所以不需要包含头文件

   {
   public:
        Point(double a = 0, double b = 0): x(a), y(b){};
        void setPoint(double a, double b) { x = a, y = b;} 
        double getX() const { return x;}
        double getY() const { return y;}
        friend ostream & operator << ( ostream &, const Point &);

    protected:
        double x;
        double y;
    }; 


类外定义Point类的成员函数
`````````````````````````````

新建point.cpp文件

.. code-block:: c++ 

   ostream & operator << ( ostream &output, const Point &p)
   {
        output << "(" << p.x <<"," <<p.y <<")"<<endl;
        return output; 
   }

Circle类
----------

声明Circle类
``````````````

新建circle.h文件

.. code-block:: c++ 

   #include "point.h"      //包含了它继承的point基类
   const double pi = 3.14159; //下面算面积的时候，pi就代表这个数值

   class Circle: public Point
   {
   public:
        Circle(double x=0, double y=0, double r=0):Point(x, y), radius(r){}
        void setRadius(double r){ radius = r ;}
        double getRadius() const { return radius;}
        double area() const { return pi * radius * radius;} 
        friend ostream & operator << ( ostream &, const Circle &);
   protected:
        double radius;
   };

类外定义Circle类的成员函数
````````````````````````````

新建circle.cpp文件

.. code-block:: c++ 

   ostream & operator << ( ostream &output, const Circle &c)
   {
      output << "圆点 = (" << c.x << "," << c.y <<")" <<", r = " <<c.radius ;
      output <<", 面积 = " << c.area() <<endl;
   }

Cylinder类
------------

声明Cylinder类
````````````````

新建Cylinder.h文件

.. code-block:: c++ 

   #include "circle.h"  //包含了它继承的Circle类
   
   class Cylinder : public Circle
   {
   public:
      Cylinder (double x, double y, double r, double h): 
          Circle(x,y,r),height(h){}

      void setHeight(double h) { height = h;}
      double getHeight() { return height;}
      double area() const
      { 
          return 2*Circle::area() + 2 * pi * radius * height; 
      }

      double volume() const
      {
          return Circle::area() * height;
      }

      friend ostream & operator << ( ostream &, const Cylinder &);

   protected:
        double height;
   };
                                 

类外定义Cylinder类的成员函数
`````````````````````````````

新建Cylinder.cpp文件

.. code-block:: c++ 

   ostream & operator << ( ostream &output, const Cylinder &cy)
   {
    output << "圆点 = (" << cy.x << "," << cy.y <<")" <<", r = " <<cy.radius;
    output << ", 表面积 =" << cy.area() << ", 体积 =" << cy.volume() <<endl;
    return output;
   } 
 
写main函数
------------

新建main.cpp文件

.. code-block:: c++ 

   #include <iostream>   //之前的做法，把类的声明和main函数都写在同一个文件，
   using namespace std;  //现在只不过是把它们分开而已，所以现在得按顺序包含进来
   #include "cylinder.h" //先声明类，再在类外定义成员函数，所以的一个先包含声明类的头文件
   #include "point.cpp"  //类外成员函数的定义，按顺序包含进来就可以了
   #include "circle.cpp"
   #include "cylinder.cpp"

   int main()
   {
        Cylinder cy(1.0, 2.0, 3.0, 4.0);
        cout << cy ;
        cy.setPoint(2.4 , 5.9);
        cy.setRadius(13);
        cy.setHeight(14);
        cout << cy;

        Point &pRef =cy;
        cout << "点 =" << pRef<<endl;

        Circle &cRef =cy;
        cout << "圆 =" <<cRef <<endl;

        return 0;
    }