pta c++ 两点间距离计算 (40分)

#include <iostream>
#include<cmath>
using namespace std;

class Point_1D

{ 
protected:

    float x;//1D 点的x坐标

public:

    Point_1D(float x):x(x){
    }

    float distance(Point_1D b){
        return fabs(x-b.x);
    }

};
/* 请在这里填写答案 */
class Point_2D:public Point_1D{
protected:

    float y;

public:
    Point_2D(float x,float y):Point_1D(x),y(y){
    }
    
    float distance(Point_2D b){
        return sqrt(pow(x-b.x,2)+pow(y-b.y,2));
    }
};

class Point_3D:public Point_2D{
protected:

    float z;

public:
    Point_3D(float x,float y,float z):Point_2D(x,y),z(z){
    }
    
    float distance(Point_3D b){
        return sqrt(pow(x-b.x,2)+pow(y-b.y,2)+pow(z-b.z,2));
    }
};
int main( ) {
    int d=0;
    float x,y,z;
    float bx,by,bz;
    while(1){
        cin>>d;
        if(d==0)break;
        if(d==1){
            cin>>x;
            cin>>bx;
            Point_1D a(x);
            Point_1D b(bx);
            cout<<"Distance from Point "<<x<<" to Point "<<bx<<" is "<<a.distance(b)<<endl;
        }else if(d==2){
            cin>>x>>y;
            cin>>bx>>by;
            Point_2D a(x,y);
            Point_2D b(bx,by);
            cout<<"Distance from Point("<<x<<","<<y<<") to Point("<<bx<<","<<by<<") is "<<a.distance(b)<<endl;
        }else{
            cin>>x>>y>>z;
            cin>>bx>>by>>bz;
            Point_3D a(x,y,z);
            Point_3D b(bx,by,bz);
            cout<<"Distance from Point("<<x<<","<<y<<","<<z<<") to Point("<<bx<<","<<by<<","<<bz<<") is "<<a.distance(b)<<endl;
        }
    }
    return 0;
}