1、只写在一个文件里时的代码

//案例2-点和圆的关系
class point//点类
{
private:int m_x;//x坐标int m_y;//y坐标public://设置xvoid setx(int x){m_x = x;}//获取xint getx(){return m_x;}//设置yvoid sety(int y){m_y = y;}//获取yint gety(){return m_y;}
};
class cirle//圆类
{
private:int m_r;//半径point m_center;//圆心public://设置半径void setr(int r){m_r = r;}//获取半径int getr(){return m_r;}//设置圆心void setcenter(point center){m_center = center;}//获取圆心point getcenter(){return m_center;}};//判断点和圆的关系
void isInCirle(Cirle&c, Point p)
{//计算点到圆心之间的距离的平方int distance = (c.getCenter().getX() - p.getX())*(c.getCenter().getX() - p.getX()) + (c.getCenter().getY() - p.getY())*(c.getCenter().getY() - p.getY());//计算圆的半径int Rdistance = c.getR()*c.getR();if (distance == Rdistance){cout << "点在圆上" << endl;}else if (distance > Rdistance){cout << "点在圆外" << endl;}else{cout << "点在圆内" << endl;}	
}
int main()
{//创建圆Cirle c1;c1.setR(10);Point center;center.setX(10);center.setY(0);c1.setCenter(center);//创建点Point p;p.setX(10);p.setY(1);//判断关系isInCirle(c1, p);}

2、分文件编写；
先建立一个头文件，命名为Point.h,放上类的成员变量和成员函数的声明；再建立一个Point.cpp的源文件写类中成员函数的具体实现，记得加上作用域。

//Point.h
#pragma once
#include<iostream>
using namespace std;
class Point//点类
{
private:int m_X;//X坐标int m_Y;//Y坐标public://设置Xvoid setX(int X);//获取Xint getX();//设置Yvoid setY(int Y);//获取Yint getY();};

//Cirle.h
#pragma once
#include<iostream>
using namespace std;
#include"Point.h"//因为Cirle类中含有Point类
class Cirle//圆类
{
private:int m_R;//半径Point m_Center;//圆心public://设置半径void setR(int R);//获取半径int getR();//设置圆心void setCenter(Point Center);//获取圆心Point getCenter();};

//Point.cpp
#include"Point.h"
void Point::setX(int X)
{m_X = X;
}
//获取X
int Point::getX()
{return m_X;
}
//设置Y
void Point::setY(int Y)
{m_Y = Y;
}
//获取Y
int Point::getY()
{return m_Y;
}

//Cirle.cpp
#include"Cirle.h"
void Cirle::setR(int R)//加上作用域
{m_R = R;
}
//获取半径
int Cirle::getR()
{return m_R;
}
//设置圆心
void Cirle::setCenter(Point Center)
{m_Center = Center;
}
//获取圆心
Point Cirle::getCenter()
{return m_Center;
}

3、在最后你要是实现的那个cpp文件里加上之前创建好的两个头文件就可以了。

#include"Cirle.h"
#include"Point.h"