C++第三次作业

#include<iostream>#include<cmath>double distance3(double a,double b,double c,double d){    double ds;    ds=sqrt((a-c)*(a-c)+(b-d)*(b-d));    return ds;}using namespace std;class Cpoint{public:    Cpoint(double xx=0,double yy=0);    double distance1(Cpoint x1);    friend double distance2(Cpoint &,Cpoint &);private:    double x;    double y;};Cpoint::Cpoint(double xx,double yy){    x=xx;    y=yy;}double Cpoint::distance1(Cpoint x1){    double d;    d=sqrt((x-x1.x)*(x-x1.x)+(y-x1.y)*(y-x1.y));    cout<<d<<endl;}double distance2(Cpoint &t1,Cpoint &t2){    double d;    d=sqrt((t1.x-t2.x)*(t1.x-t2.x)+(t1.y-t2.y)*(t1.y-t2.y));    cout<<d<<endl;}int main(){    Cpoint c1(2,2);    Cpoint c2(1,1);    c1.distance1(c2);    distance2(c1,c2);    cout<<distance3(1,1,2,2)<<endl;}