第七周任务

#include<iostream>   #include<cmath>   using namespace std;  class Cpoint  {  private:      double x;      double y;  public:      Cpoint(double xx=0,double yy=0):x(xx),y(yy){}      double distance1(Cpoint &);      friend double distance2(Cpoint &,Cpoint &);      double getX(){return x;}      double getY(){return y;}  };  double distance3(Cpoint &,Cpoint &);  double Cpoint::distance1(Cpoint &p)  {      double dx=(x-p.x),dy=(y-p.y);      return sqrt(dx*dx+dy*dy);  }  double distance2(Cpoint &p1,Cpoint &p2)  {      double dx=(p1.x-p2.x),dy=(p1.y-p2.y);      return sqrt(dx*dx+dy*dy);  }  double distance3(Cpoint &p1,Cpoint &p2)  {      double dx=(p1.getX()-p2.getX()),dy=(p1.getY()-p2.getY());      return sqrt(dx*dx+dy*dy);  }  int main()  {      Cpoint p1(10,13),p2(-2,6);      cout<<"1.成员函数："<<p1.distance1(p2)<<endl;     cout<<"2.友元函数："<<distance2(p1,p2)<<endl;      cout<<"3.一般函数："<<distance3(p1,p2)<<endl;      return 0;  }