no appropriate default constructor available

[thorster]

I get this compiler error:
error C2512: 'Graph_lib::Ellipse': no appropriate default constructor available
I'm trying to create a class Arc that inherits from Ellipse. I don't understand why I get this compiler error. Any hints? (Perhaps should Arc inherit from Shape instead?)

struct Ellipse : Shape {
	Ellipse(Point p, int ww, int hh)	// center, min, and max distance from center
		:w{ ww }, h{ hh } {
		add(Point{ p.x - ww, p.y - hh });
	}

	void draw_lines() const;

	Point center() const { return{ point(0).x + w, point(0).y + h }; }
	Point focus1() const { return{ center().x + int(sqrt(double(w*w - h*h))), center().y }; }
	Point focus2() const { return{ center().x - int(sqrt(double(w*w - h*h))), center().y }; }

	void set_major(int ww) { w = ww; }
	int major() const { return w; }
	void set_minor(int hh) { h = hh; }
	int minor() const { return h; }
private:
	int w;
	int h;
};

struct Arc : Ellipse {
	Arc(Point p, int ww, int hh, double saa, double eaa)
		: w{ ww }, h{ hh }, sa{ saa }, ea{ eaa } {
		add(Point{ p.x - ww, p.y - hh });
	}
	void draw_lines() const;

private:
	int w; // Width
	int h; // Heigth
	double sa; // Start angle
	double ea; // End angle
	};

[gunnerfunner]

Can you show us how Graph_lib::Ellipse uses Ellipse objects? Is it in line with the Ellipse ctor defined in struct Ellipse?