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// Circle C2D                                                                 C#
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public struct C2D
{
    const double eps = 1e-9;
    static bool eq(double a, double b) { return Math.Abs(a - b) < eps; }
    static bool ge(double a, double b) { return a - b > -eps; }
    static bool le(double a, double b) { return b - a > -eps; }
    static bool gt(double a, double b) { return a - b > eps; }
    static bool lt(double a, double b) { return b - a < eps; }
	
    public P2D C { get; set; }
    public double R { get; set; }
    public C2D(double x, double y, double r) { C = new P2D(x, y); R = r; }
    public C2D(P2D c, double r) { C = c; R = r; }
    public C2D Copy() { return new C2D(C.Copy(), R); }
    public bool Inside(P2D p) { return le((p - C).Abs(), R); }
    public double Area() { return Math.PI * R * R; }
    public P2D[] ToPolygon(int n)
    {
        P2D[] pgon = new P2D[n];
        for (int i = 0; i < n; i++)
            pgon[i] = new P2D(C.X + R * Math.Cos(Math.PI * 2 * i / n),
                              C.Y + R * Math.Sin(Math.PI * 2 * i / n));
        return pgon;
    }
}

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