计算三角形的周长和面积的类

class shape
{
public:
    virtual float perimeter() const{ return 0; }
    virtual float area()const { return 0; }
    virtual const char* name()const
    {
        return "抽象图形";
    }
};

class point
{
    float x;
    float y;
public:
    point(float x0, float y0) :x(x0), y(y0){}
    float getX()const { return x; }
    float getY()const { return y; }
};

class triangle :public shape
{
    point point1, point2, point3;
public:
    triangle(point p1, point p2, point p3) :point1(p1), point2(p2), point3(p3){}
    float perimeter()const;
    float area()const;
    const char* name()const{ return "三角形"; }
};

float length(point p1, point p2)
{
    return sqrt((p1.getX() - p2.getX())*(p1.getX() - p2.getX()) + (p1.getY() - p2.getY())*(p1.getY() - p2.getY()));
}

float triangle::perimeter()const
{
    float x = length(point1, point2);
    float y = length(point1, point3);
    float z = length(point3, point2);
    return length( point1, point2) + length( point1,  point3) + length( point2,  point3);
}
float triangle::area()const
{
    float s = perimeter() / 2.0;
    return sqrt(s*(s - length(point1, point2))
        *(s - length(point2, point3))
        *(s - length(point3, point1)));
}

void show(shape& shape)
{
    cout << "此图形是一个 " << shape.name() << ",周长= " << shape.perimeter() <<
        ", 面积=" << shape.area() << endl;
}
int _tmain()
{
    shape s;
    triangle tri(point(0, 2), point(2, 0), point(0, 0));
    show(s);
    show(tri);
    return 0;



}