// Source: "Software Design ...", John A Robinson, Newnes, 2004, page 129.
const int max_dimensions = 8;
class real_vector
	{
	int dimensions;
	double vector_base[max_dimensions];	// The vector itself is stored in this array
public:
	real_vector(const int ndim)		// The constructor takes a parameter which specifies
						// how many dimensions this vector is to have
		{
		if (ndim > max_dimensions)
			dimensions = max_dimensions;
		else
			dimensions = ndim; 
		}
	~real_vector()				// The destructor does not have to do any tidying up,
						// so it is empty.
		{ 
		}
	int set_component(const int comp, const double value);
	int get_component(const int comp, double& value) const;
	int tell_num_dimensions() const
		{
		return(dimensions);
		}
	real_vector sum_with_me(const real_vector& u);  // Returns a vector sum 
	double dot_with_me(const real_vector& u);       // Returns dot product
	};

int real_vector::set_component(const int comp, const double value)
	{
	if ((comp < 0) || (comp > dimensions-1))
		return(-1);
	vector_base[comp] = value;
	return(0);
	}
int real_vector::get_component(const int comp, double& value) const
	{
	if ((comp < 0) || (comp > dimensions-1))
		return(-1);
	value = vector_base[comp]; 
	return(0);
	}
real_vector real_vector::sum_with_me(const real_vector& u)
// Returns a vector that is the sum of this object and the 
// vector given as a parameter
	{
	real_vector sum(dimensions);
	// Set up a vector with the same number
	// of dimensions as me.
	if (u.tell_num_dimensions() != dimensions)            		// ***             
	// If the vector I am being summed with has a different number of dimensions
		return(sum); // Essentially an error return -- zero vector
	for (int i = 0; i < dimensions; i++)				      
		sum.vector_base[i] = u.vector_base[i] + vector_base[i];	// +++
	return(sum);
	}
double real_vector::dot_with_me(const real_vector& u)         
// Returns dot product of this object and the vector given as a parameter.
// (The dot product multiplies each pair of components, then sums the results)
	{
	double dot_product = 0;
	if (u.dimensions != dimensions)
		return(dot_product);
	for (int i = 0; i < dimensions; i++)
		dot_product += u.vector_base[i] * vector_base[i]; 	// +++
	return(dot_product);
	}


#include <iostream>
using namespace std;
// Next line commented out in online version because all code is in this one file.
// #include "vec_def.h"				// Including the above vector class definition file
int main()
	{
	real_vector a(3), b(3);			// These will be set up as three dimensional vectors
	a.set_component(0,0.0);
	a.set_component(1,1.0);
	a.set_component(2,2.0);
	b.set_component(0,3.0);
	b.set_component(1,4.0);
	b.set_component(2,5.0);
	real_vector c = a.sum_with_me(b);
	double x, y, z;
	c.get_component(0,x);
	c.get_component(1,y);
	c.get_component(2,z); 
	cout << x << ", " << y << ", " << z << "\n"; 
	return 0;
	}