编写一个名为door的类，其中定义两个公有浮点型成员变量height和width， 其赋其缺省值分别为 2.0 和 1.5

#include <iostream>

class door
{
public:
    double height;
    double width;

    explicit door( double height=2.0, double width=1.5 ) : height(height), width(width)
    {
        std::cout << "The door is created…\n";
    }
    door( const door& rhs ) :  height(rhs.height), width(rhs.width)
    {
        std::cout << "The door is created…\n";
    }
    door( door&& rhs ) noexcept = default;

    ~door()
    {
        std::cout << "The door is destroyed…\n";
    }

    double perimeter() const noexcept
    {
        return 2*(height+width);
    }
    double acreage() const noexcept
    {
        return height*width;
    }
};

std::ostream& operator<<( std::ostream& os, const door& rhs )
{
    return os << "{ height=" << rhs.height << ", width=" << rhs.width << " }";
}

using namespace std;

int main( void )
{
    {
        door a;
        cout << a << endl;

        door b{ 3, 4 };
        cout << b << endl;

        door c = b;
        cout << b << endl;

        cout << "perimeter: " << c.perimeter() << endl;
        cout << "acreage: " << c.acreage() << endl;
    }
}