#include <stdio.h>                                          /* line.c */
#include <math.h>

typedef struct { double x, y; } Point;

typedef struct { Point from, to; } Line;

double lineLength(const Line * l) { /* pass by reference cheaper than copying */
  double dx = l->to.x - l->from.x;
  double dy = l->to.y - l->from.y;
  return sqrt( dx * dx + dy * dy );
}

int main() {
  Line u = { {3.0, 4.0}, {7.0, 1.0} };               /* nested structure initialisation */
  printf( "length = %f\n", lineLength( &u ) );
  printf( "sizeof( Line ) = %d\n", sizeof( Line ) );
  return 0;
}