面向对象——案例练习（1）求圆的周长和面积

面向对象与面向过程：

面向过程：人.吃（饭）
面向对象：吃（人，饭）

方法一：面向过程

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
using namespace std;

//圆的周长
double getCircleGirth(double r)
{
    return 2 * 3.14*r;
}

//圆的面积
double getCircleArea(double r)
{
    return 3.14*r*r;
}

int main(void)
{
    double r=10;
    double girth=0;
    double area=0;
    
    girth = getCircleGirth(r);
    area = getCircleArea(r);
    
    cout << "圆的半径：" << r << endl;
    cout << "圆的周长：" << girth << endl;
    cout << "圆的面积：" << area << endl;

    return 0;
}

方法二：面向对象

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
using namespace std;

class Circle
{
public:
　　 //圆的周长
    double getCircleGirth()
    {
        return 2 * 3.14*m_r;
    }
　　 //圆的面积
    double getCircleArea()
    {
        return 3.14*m_r*m_r;
    }
    void set(double r)
    {
        m_r = r;
    }
    double get()
    {
        return m_r;
    }
private:
    int m_r;
};

int main(void)
{
    Circle c;
    double r;
    double girth;
    double area;
    
    c.set(10);
    girth = c.getCircleGirth();
    area = c.getCircleArea();
    
    cout << "圆的半径：" << c.get() << endl;
    cout << "圆的周长：" << girth << endl;
    cout << "圆的面积：" << area << endl;

    return 0;
}