Answer to Question 04C-2

#include <cmath>
using namespace std;

// distance(x1, y1, x2, y2) returns the distance between
// points (x1, y1) and (x2, y2) in the plane.

double distance(double x1, double y1, double x2, double y2)
{
  double deltaX = x1 - x2;
  double deltaY = y1 - y2;
  return sqrt(deltaX*deltaX + deltaY*deltaY);
}