將類的定義放在頭文件中，把成員函數的實現代碼放在一個cpp文件中

寫這種.h和.cpp文件分開的大程序，雖然對很多人來說很簡單，對自己來說算是第一次吧，好好學C++，加油~

題目：定義Point類，由Point派生出Circle類，再由Circle派生出Cylinder類。將類的定義部分分別作為3個頭文件，對他們的成員函數的定義分別作為3個源文件

1、Point.h文件

#ifndef POINT_H
#define POINT_H
#include<iostream>    //頭文件也需要包含這個
using namespace std;

class Point
{
protected:
    float x, y;
public:
    Point(float a = 0, float b = 0);     //帶默認參數的構造函數的聲明
    float getX();
    float getY();
    void setPoint(float, float);
    friend ostream& operator<<(ostream &output, const Point &p);    //運算符重載
    
};

#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);    //運算符重載
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)    //重載運算符“<<”
{
    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)    //運算符重載
{
    output << "圓心：（" << c.x << "," << c.y << ")   半徑：" << c.radius << "     面積：" << 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() 屬於同名覆蓋
{
    output << "圓心：(" << cy.x << "," << cy.y << ")   半徑：" << cy.radius << "  高：" << cy.height << "\n                  面積: " << cy.area() << "   體積:" << cy.volume() << endl;
    return output;
}

7、main函數

//習題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;
}

 

運行結果：

總結：

1、在寫頭文件是要注意寫

#ifndef POINT_H
#define POINT_H

……

#endif

可以避免多次包含同一頭文件，防止重定義

2、基本的頭文件要寫在.h文件中