/* This program reads in the x and y coordinates of NUM_POINTS points from
   a file points.dat.  If then computes the length of the connect-the-dot
   path from point 0 to point 1 to ... point NUM_POINTS - 1.
*/

#include<iostream.h>
#include<fstream.h>
#include<math.h>

const int NUM_POINTS = 10;

double line_seg_length (double, double, double, double);
double path_length(double[], double[]);

void main(){

  ifstream infile("points.dat");

  double x[NUM_POINTS], y[NUM_POINTS];

  for (int i = 0; i< NUM_POINTS; i++)
    infile >> x[i] >> y[i];

  cout << "The length of the connect-the-dots path starting at\npoint 0"
       << " and ending at point " << NUM_POINTS - 1 << " is " 
       << path_length(x,y) << ".\n";
}

double line_seg_length (double x1, double y1, double x2, double y2){
  return sqrt(pow(x2-x1,2) + pow(y2-y1,2));
}

/* Remember there are NUM_POINTS points, but only NUM_POINTS - 1 line
   segments to compute the length of.  This is reflected in the loop
   below (see how the alternate version commented out below it differs).
*/

double path_length (double x[], double y[]){

  double length = 0;

  for (int i=0; i < NUM_POINTS - 1; i++)
    length += line_seg_length(x[i], y[i], x[i+1], y[i+1]);
  
  /* the previous loop is equivalent to ...
  for (int i=1; i < NUM_POINTS; i++)
    length += line_seg_length(x[i-1], y[i-1], x[i], y[i]);
  */

  return length;
}