#include<iostream.h>

class Vector {
public:
  Vector(unsigned length);
  Vector(double *data, unsigned length);
  double& operator() (unsigned entry);
  double  operator() (unsigned entry) const;

 ~Vector();
  

  Vector& operator= (Vector& v);
  Vector& operator+= (Vector& v);
  Vector& operator-= (Vector& v);
  Vector& operator*= (double a);
  unsigned length() {return length_; };
  void clear(){for(unsigned i=0;i<length_;i++) data_[i]=0;};
  bool rescale(unsigned length);
  // ...
protected:
  unsigned length_;
  double* data_;
};

inline
Vector& Vector::operator= (Vector& v){
	unsigned l = v.length();
	data_ = new double[l];
	for(unsigned i=1;i<=l;i++)
		data_[i-1] = v(i);
}

inline
Vector& Vector::operator+= (Vector& v){
	unsigned l = v.length();
	if(l>length_) l = length_; //若長度不等，只加有效部分 
	for(unsigned i=1;i<=l;i++)
		data_[i-1] += v(i);
}

inline
Vector& Vector::operator-= (Vector& v){
	unsigned l = v.length();
	if(l>length_) l = length_; //若長度不等，只加有效部分 
	for(unsigned i=1;i<=l;i++)
		data_[i-1] -= v(i);
}

inline
Vector& Vector::operator*= (double a){
	for(unsigned i=1;i<=length_;i++)
		data_[i-1] *= a;
}



inline
Vector::Vector(unsigned length)
  : length_ (length),
    data_ (new double[length])
{
  if (length == 0)
  void();
//     throw BadIndex("Vector constructor has 0 size");
  unsigned l = length;
  for(unsigned i=0;i<l;i++) data_[i]=0.0;
}

inline
Vector::Vector(double* data, unsigned length)
	: length_ (length),
	  data_ (data)
{}

inline
bool Vector::rescale(unsigned length)
{
	if(length==length_) return false;
	length_ = length;
	delete[] data_;
	data_ = new double[length];
	clear();
	return true;
}

inline
Vector::~Vector()
{
  delete[] data_;
}

inline
double& Vector::operator() (unsigned entry)
{
  if (entry > length_)    void();
//     throw BadIndex("Vector subscript out of bounds");
  return data_[entry-1];
}

inline
double Vector::operator() (unsigned entry) const
{
  if (entry > length_)    void();
//     throw BadIndex("Vector subscript out of bounds");
  return data_[entry-1];
} 

/*
int main()
{
  Vector v(10);
  v(5) = 106.15;
  v *=3;
  cout << v(5);
   getchar();
} 
*/