C++ 与 PHP - 面向对象的问题：

面向对象编程是现代编程语言中的一种重要编程范式，它可以提高代码的复用性和可维护性。C++和PHP都是支持面向对象编程的流行语言，它们在面向对象思想的实现上有一些共同点，但也存在一些差异。本文将就C++和PHP在面向对象编程中的问题进行探讨，并通过案例代码进行说明。

cpp
class Circle {
    private:
        double radius;
    
    public:
        void setRadius(double r) {
            radius = r;
        }
        
        double getRadius() {
            return radius;
        }
        
        double getArea() {
            return 3.14 * radius * radius;
        }
};

php
class Circle {
    private $radius;
    
    public function setRadius($r) {
        $this->radius = $r;
    }
    
    public function getRadius() {
        return $this->radius;
    }
    
    public function getArea() {
        return 3.14 * $this->radius * $this->radius;
    }
}

cpp
class Shape {
    protected:
        double width;
        double height;
    
    public:
        void setWidth(double w) {
            width = w;
        }
        
        void setHeight(double h) {
            height = h;
        }
};
class Rectangle : public Shape {
    public:
        double getArea() {
            return width * height;
        }
};

php
class Shape {
    protected $width;
    protected $height;
    
    public function setWidth($w) {
        $this->width = $w;
    }
    
    public function setHeight($h) {
        $this->height = $h;
    }
}
class Rectangle extends Shape {
    public function getArea() {
        return $this->width * $this->height;
    }
}

cpp
class Shape {
    public:
        virtual double getArea() {
            return 0;
        }
};
class Rectangle : public Shape {
    private:
        double width;
        double height;
    
    public:
        Rectangle(double w, double h) {
            width = w;
            height = h;
        }
        
        double getArea() {
            return width * height;
        }
};
class Circle : public Shape {
    private:
        double radius;
    
    public:
        Circle(double r) {
            radius = r;
        }
        
        double getArea() {
            return 3.14 * radius * radius;
        }
};

php
interface Shape {
    public function getArea();
}
class Rectangle implements Shape {
    private $width;
    private $height;
    
    public function __construct($w, $h) {
        $this->width = $w;
        $this->height = $h;
    }
    
    public function getArea() {
        return $this->width * $this->height;
    }
}
class Circle implements Shape {
    private $radius;
    
    public function __construct($r) {
        $this->radius = $r;
    }
    
    public function getArea() {
        return 3.14 * $this->radius * $this->radius;
    }
}