#define XMAX 640
#define YMAX 480

class Vector {
      friend Vector operator+(const Vector &a, const Vector &b);
      friend Vector operator-(const Vector &a, const Vector &b);
      friend Vector operator*(double a, const Vector &b);
      friend Vector operator/(const Vector &a, double b);
      friend double mag(const Vector &r);

      public:
	      double x;
	      double y;
	     Vector(double i=0, double j=0);
	     Vector(const Vector &value);
	     ~Vector();
	     void set(double i,	double j);
};

void swap(Vector &a, Vector &b);
Vector Vrand();
Vector Prand();

const Vector	V0(0,0),
		CENTER(XMAX/2,YMAX/2);