C++ 组合 (Composition)的介绍与实例

#ifndef PROJECT5_DOT_H
#define PROJECT5_DOT_H

#include <iostream>
using namespace std;

class Dot {
public:
    double x, y;
    Dot(double a, double b) : x(a), y(b) {};
    void show() {
        cout << "x: " << x << endl;
        cout << "y: " << y << endl;
    };
};

#endif //PROJECT5_DOT_H

#ifndef PROJECT5_LINE_H
#define PROJECT5_LINE_H

#include "Dot.h"

class Line : public Dot {
private:
    Dot d1;
    Dot d2;
public:
    Line(const Dot &d1, const Dot &d2) : Dot(0, 0), d1(d1), d2(d2) {
        x = (d1.x + d2.x) / 2;
        y = (d1.y + d2.y) / 2;
    }

    void show(){
        Dot::show();
        cout << "dot1: (" << d1.x << ", " << d1.y << ")" << endl;
        cout << "dot2: (" << d2.x << ", " << d2.y << ")" << endl;
    }
};

#endif //PROJECT5_LINE_H

#include <iostream>
#include "Dot.h"
#include "Line.h"
using namespace std;

int main() {
    double a, b;
    cout << "Input Dot1: \n";
    cin >> a >> b;
    Dot dot1(a,b);
    cout << "Input Dot2: \n";
    cin >> a >> b ;
    Dot dot2(a,b);
    Line l1(dot1, dot2);
    l1.show();

    return 0;
}