#include <stdio.h>
#include <memory.h>
#include <stdint.h>
#define MAX 10


typedef struct {
  int x, y;
} pointworm_t;


pointworm_t worm[MAX] = {
  5,5,
  5,4,
  4,4,
  3,4,
  2,4,
  2,3,
}, newhead;

typedef struct {
  pointworm_t * begin, * end;
} vec_t;



typedef enum {SET, GET} vec_ctx_state;

vec_t vec_ctx(vec_ctx_state state, vec_t set) {
  static vec_t vec = {0};
  return (state == GET) ? vec : (vec = set);
}

inline  void set_ctx(vec_t vec) {
  vec_ctx(SET, vec);
}

inline  vec_t get_ctx(void) {
  return vec_ctx(GET, (vec_t){0});
}

inline  uintmax_t vec_size_noctx(vec_t v) {
  return (uintptr_t)((void *)v.end - (void *)v.begin);
}

inline  uintmax_t vec_size(void) {
  vec_t v = get_ctx(); return vec_size_noctx(v);
}

inline  uintmax_t vec_elem_size_noctx(vec_t v) { return sizeof(typeof(*v.begin)); }

inline uintmax_t vec_elem_size(void) {
  vec_t v = get_ctx(); return vec_elem_size_noctx(v);
}

inline void vec_movesnake(void) {
  vec_t v = get_ctx();
  memmove(v.begin + 1, v.begin, vec_size() - vec_elem_size());
};

inline  void vec_set_head(pointworm_t pnewhead) {
  *(get_ctx().begin) = pnewhead;
}

inline pointworm_t add(pointworm_t a, pointworm_t b) {
  return (pointworm_t){a.x + b.x, a.y + b.y};
}

inline pointworm_t create_point(int32_t x, int32_t y) {
  return (pointworm_t){x, y};
}

inline pointworm_t vec_getn(uintmax_t n) {
  return *(get_ctx().begin + n);
}

inline pointworm_t * vec_end(void) {
  return get_ctx().end;
}

inline pointworm_t * vec_begin(void) {
  return get_ctx().begin;
}

inline vec_print(typeof(stdout) out) {
  typeof(vec_begin()) it = vec_begin(), end = vec_end();
  do {
    fprintf(out, "%d, %d\n", it->x, it->y);
  } while(++it != end);
}

int32_t main(void) {
  set_ctx((vec_t){worm, worm + 6});

  newhead = add(vec_getn(0), create_point(1, 0));
  vec_movesnake();
  vec_set_head(newhead);
  vec_print(stdout);

  return 0;
}