#include <stdio.h>
#include <math.h>

/* the definition of point struct */
typedef struct {
  double x;
  double y;
} point;

/* the distance function */
double distance( point a, point b ) {
  double delta_x, delta_y;
  delta_x = a.x-b.x;
  delta_y = a.y-b.y;
  return sqrt( delta_x*delta_x + delta_y*delta_y );
}


int main ( void ) {
  point m,n;
  double dist;

  /* first point is m=(1,2) */
  m.x = 1;
  m.y = 2;
  /* second point is n=(4,6) */
  n.x = 4;
  n.y = 6;

  dist = distance(m,n);

  printf( "The distance is %g.\n", dist );

  return 0;
}