class Vector
{
public:
  Vector( double x = 0, double y = 0, double z = 0 );
  double x() const;
  double y() const;
  double z() const;
  Vector& operator=( const Vector& u );

private:
  double x_, y_, z_;
};

Vector operator+(const Vector&, const Vector&);
double operator*(const Vector&, const Vector&);

#include <iostream>
ostream& operator<<( ostream& , const Vector& );