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

 1 #ifndef POINT_H
 2 #define POINT_H
 3 #include<iostream>    //头文件也需要包含这个
 4 using namespace std;
 5
 6 class Point
 7 {
 8 protected:
 9     float x, y;
10 public:
11     Point(float a = 0, float b = 0);     //带默认参数的构造函数的声明
12     float getX();
13     float getY();
14     void setPoint(float, float);
15     friend ostream& operator<<(ostream &output, const Point &p);    //运算符重载
16
17 };
18
19 #endif

2、Circle.h文件

 1 #ifndef CIRCLE_H
 2 #define CIRCLE_H
 3
 4 #include "Point.h"
 5
 6 class Circle:public Point
 7 {
 8 public:
 9     Circle(float a = 0, float b = 0, float r = 0);
10     float getR();
11     void setR(float r);
12     float area();
13     friend ostream& operator<<(ostream &output, Circle &c);    //运算符重载
14 protected:
15     float radius;
16 };
17
18 #endif

3、Cylinder.h文件

 1 #ifndef CYLINDER_H
 2 #define CYLINDER_H
 3
 4 #include "Circle.h"
 5
 6 class Cylinder :public Circle
 7 {
 8 public:
 9     Cylinder(float a = 0, float b = 0, float r = 0, float h = 0);
10     void setH(float h);
11     float getH();
12     float area();
13     float volume();
14     friend ostream& operator<<(ostream &, Cylinder &);
15 private:
16     float height;
17 };
18
19 #endif

4、Point.cpp文件

 1 #include<iostream>
 2 #include"Point.h"
 3 using namespace std;
 4
 5 Point::Point(float a, float b)
 6 {
 7     x = a;
 8     y = b;
 9 }
10
11 float Point::getX()
12 {
13     return x;
14 }
15 float Point::getY()
16 {
17     return y;
18 }
19 void Point::setPoint(float a, float b)
20 {
21     x = a;
22     y = b;
23 }
24
25 ostream& operator<<(ostream &output, const Point &p)    //重载运算符“<<”
26 {
27     output << "(" << p.x << "," << p.y << ")" << endl;
28     return output;
29 }

5、Circle.cpp文件

 1 #include<iostream>
 2 #include"Circle.h"
 3 using namespace std;
 4
 5 Circle::Circle(float a, float b, float r) :Point(a, b), radius(r) { }
 6
 7 float Circle::getR()
 8 {
 9     return radius;
10 }
11
12 void Circle::setR(float r)
13 {
14     radius = r;
15 }
16
17 float Circle::area()
18 {
19     return 3.14*radius*radius;
20 }
21
22 ostream& operator<<(ostream &output, Circle &c)    //运算符重载
23 {
24     output << "圆心：（" << c.x << "," << c.y << ")   半径：" << c.radius << "     面积：" << c.area() << endl;
25     return output;
26 }

　　6、Cylinder.cpp文件

 1 #include<iostream>
 2 #include"Cylinder.h"
 3 using namespace std;
 4
 5 Cylinder::Cylinder(float a, float b, float r, float h) :Circle(a, b, r), height(h) { }
 6
 7 void Cylinder::setH(float h)
 8 {
 9     height = h;
10 }
11
12 float Cylinder::getH()
13 {
14     return height;
15 }
16
17 float Cylinder::area()
18 {
19     return 2 * Circle::area() + 2 * 3.14*radius*height;
20 }
21
22 float Cylinder::volume()
23 {
24     return Circle::area()*height;
25 }
26
27 ostream& operator<<(ostream &output, Cylinder &cy)    //cy.area() 属于同名覆盖
28 {
29     output << "圆心：(" << cy.x << "," << cy.y << ")   半径：" << cy.radius << "  高：" << cy.height << "\n                  面积: " << cy.area() << "   体积:" << cy.volume() << endl;
30     return output;
31 }

7、main函数

 1 //习题6.1
 2 //#include<iostream>
 3 //#include"Point.h"
 4 //#include"Circle.h"
 5 #include"Cylinder.h"
 6 //using namespace std;
 7
 8 int main()
 9 {
10     Cylinder cy1(3, 3, 5, 6);
11     cout << "original cylinder:" << cy1 << endl;
12     cy1.setPoint(-2, -2);
13     cy1.setR(8);
14     cy1.setH(10);
15     cout << "new cylinder: " << cy1 << endl;
16     Point &p1 = cy1;
17     cout << "as a point: " << p1 << endl;
18     Circle &c1 = cy1;
19     cout << "as a circle: " << c1 << endl;
20     return 0;
21 }

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