C++设计并测试一个矩形类，属性为矩形的左下与右上角的坐标，矩形水平放置，操作为计算矩形周长和面积，类对象的数据由友元函数来进行访问

#include<iostream>
using namespace std;

class Rectangle {
    friend double getPerimeter(Rectangle r);
    friend double getArea(Rectangle r);
    private:
        double x1, y1, x2, y2;
    public:
        Rectangle(double x1, double y1, double x2, double y2) {
            this->x1 = x1;
            this->y1 = y1;
            this->x2 = x2;
            this->y2 = y2;
        }
};

double getPerimeter(Rectangle r) {
    double length = r.y2 - r.y1;
    double width = r.x2 - r.x1;
    return 2 * (length + width);
}

double getArea(Rectangle r) {
    double length = r.y2 - r.y1;
    double width = r.x2 - r.x1;
    return length * width;
}

int main() {
    Rectangle r(0, 0, 4, 3);
    cout << "Perimeter: " << getPerimeter(r) << endl;
    cout << "Area: " << getArea(r) << endl;
    return 0;
}