class Vector
{ public:
     Vector() {}
     Vector(float a, float b);
     Vector operator-(Vector a);
     float inner(Vector a);
     int is_parallel(Vector a);
     int nonzero()
         { return ( x != 0.0 || y != 0.0 ); }
     void display();
     /* other members not shown */
 private:
     float x, y;
};