将类的定义放在头文件中，把成员函数的实现代码放在一个cpp文件中

写这种.h和.cpp文件分开的大程序，虽然对很多人来说很简单，对自己来说算是第一次吧，好好学C++，加油~

题目：定义Point类，由Point派生出Circle类，再由Circle派生出Cylinder类。将类的定义部分分别作为3个头文件，对他们的成员函数的定义分别作为3个源文件

1、Point.h文件

#ifndef POINT_H
#define POINT_H
#include<iostream>    //头文件也需要包含这个
using namespace std;

class Point
{
protected:
    float x, y;
public:
    Point(float a = 0, float b = 0);     //带默认参数的构造函数的声明
    float getX();
    float getY();
    void setPoint(float, float);
    friend ostream& operator<<(ostream &output, const Point &p);    //运算符重载
    
};

#endif

2、Circle.h文件

#ifndef CIRCLE_H
#define CIRCLE_H

#include "Point.h"

class Circle:public Point
{
public:
    Circle(float a = 0, float b = 0, float r = 0);
    float getR();
    void setR(float r);
    float area();
    friend ostream& operator<<(ostream &output, Circle &c);    //运算符重载
protected:
    float radius;
};

#endif

3、Cylinder.h文件

#ifndef CYLINDER_H
#define CYLINDER_H

#include "Circle.h"

class Cylinder :public Circle
{
public:
    Cylinder(float a = 0, float b = 0, float r = 0, float h = 0);
    void setH(float h);
    float getH();
    float area();
    float volume();
    friend ostream& operator<<(ostream &, Cylinder &);
private:
    float height;
};

#endif

4、Point.cpp文件

#include<iostream>
#include"Point.h"
using namespace std;

Point::Point(float a, float b)
{
    x = a;
    y = b;
}

float Point::getX()
{
    return x;
}
float Point::getY()
{
    return y;
}
void Point::setPoint(float a, float b)
{
    x = a;
    y = b;
}

ostream& operator<<(ostream &output, const Point &p)    //重载运算符“<<”
{
    output << "(" << p.x << "," << p.y << ")" << endl;
    return output;
}

5、Circle.cpp文件

#include<iostream>
#include"Circle.h"
using namespace std;

Circle::Circle(float a, float b, float r) :Point(a, b), radius(r) { }

float Circle::getR()
{
    return radius;
}

void Circle::setR(float r)
{
    radius = r;
}

float Circle::area()
{
    return 3.14*radius*radius;
}

ostream& operator<<(ostream &output, Circle &c)    //运算符重载
{
    output << "圆心：（" << c.x << "," << c.y << ")   半径：" << c.radius << "     面积：" << c.area() << endl;
    return output;
}

　　6、Cylinder.cpp文件

#include<iostream>
#include"Cylinder.h"
using namespace std;

Cylinder::Cylinder(float a, float b, float r, float h) :Circle(a, b, r), height(h) { }

void Cylinder::setH(float h)
{
    height = h;
}

float Cylinder::getH()
{
    return height;
}

float Cylinder::area()
{
    return 2 * Circle::area() + 2 * 3.14*radius*height;
}

float Cylinder::volume()
{
    return Circle::area()*height;
}

ostream& operator<<(ostream &output, Cylinder &cy)    //cy.area() 属于同名覆盖
{
    output << "圆心：(" << cy.x << "," << cy.y << ")   半径：" << cy.radius << "  高：" << cy.height << "
                  面积: " << cy.area() << "   体积:" << cy.volume() << endl;
    return output;
}

7、main函数

//习题6.1
//#include<iostream>
//#include"Point.h"
//#include"Circle.h"
#include"Cylinder.h"
//using namespace std;

int main()
{
    Cylinder cy1(3, 3, 5, 6);
    cout << "original cylinder:" << cy1 << endl;
    cy1.setPoint(-2, -2);
    cy1.setR(8);
    cy1.setH(10);
    cout << "new cylinder: " << cy1 << endl;
    Point &p1 = cy1;
    cout << "as a point: " << p1 << endl;
    Circle &c1 = cy1;
    cout << "as a circle: " << c1 << endl;
    return 0;
}

运行结果：

总结：

1、在写头文件是要注意写

#ifndef POINT_H
#define POINT_H

……

#endif

可以避免多次包含同一头文件，防止重定义

2、基本的头文件要写在.h文件中