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



typedef struct point {
  double x, y;
} point;


/*
Nested anonymous struct declaration compiles with MS extensions only.
So you have to use -fms-extensions flag with gcc / clang.
C11 standard allows no typedef in the nested anonymous declaration :(
*/
typedef struct {
  struct point;
  double z;
} threepoint;


double threelength(threepoint p) {
  return sqrt(p.x * p.x + p.y * p.y + p.z * p.z);
}


int main () {

  threepoint p = {.x = 3, .y = 0, .z = 4};
  printf("p is %g units from the origin\n", threelength(p));

}