Field map example

// main.c
#include <stdbool.h>
#include "map.h"

int main(void) {
  map_init(true);
  map_display();
  map_put(MAP_HORIZONTAL / 2, MAP_VERTICAL / 2, 'x');
  map_display();
  map_move(MAP_HORIZONTAL / 2, MAP_VERTICAL / 2, 0, 0);
  map_display();
  map_delete();
}

// map.h
#ifndef MAP_H_
#define MAP_H_
#include <stdbool.h>
#include <stddef.h>
#define MAP_HORIZONTAL 7
#define MAP_VERTICAL 7
void map_init(bool);
void map_delete(void);
void map_display(void);
void map_put(size_t, size_t, char);
char map_get(size_t, size_t);
void map_move(size_t, size_t, size_t, size_t);
#endif /* MAP_H_ */

// map_inner.h
#ifndef MAP_INNER_H_
#define MAP_INNER_H_
#ifdef IN_MAP
#include <stdbool.h>
#include <stddef.h>
static char *map;
static bool map_invalid_coord(size_t, size_t);
#endif /* IN_MAP */
#endif /* MAP_INNER_H_ */

// map.c
#include <stdio.h>
#include <stdlib.h>
#define IN_MAP
#include "map.h"
#include "map_inner.h"

void map_init(bool force) {
  if (!force) {
    return;
  }
  map = malloc(MAP_HORIZONTAL * MAP_VERTICAL);
  char c;
  for (size_t j = 0; j < MAP_VERTICAL; ++j) {
    for (size_t i = 0; i < MAP_HORIZONTAL; ++i) {
      if (j == 0 || j == MAP_VERTICAL - 1) {
        c = '*';
      } else if (i == 0 || i == MAP_HORIZONTAL - 1) {
        c = '*';
      } else {
        c = ' ';
      }
      map_put(i, j, c);
    }
  }
}

void map_delete(void) {
  free(map);
}

void map_put(size_t x, size_t y, char c) {
  if (map_invalid_coord(x, y)) {
    return;
  }
  map[y * MAP_HORIZONTAL + x] = c;
}

void map_display(void) {
  for (size_t j = 0; j < MAP_VERTICAL; ++j) {
    for (size_t i = 0; i < MAP_HORIZONTAL; ++i) {
      printf("%c", map_get(i, j));
    }
    puts("");
  }
  puts("");
}

char map_get(size_t x, size_t y) {
  if (map_invalid_coord(x, y)) {
    return '#'; // for error
  }
  return map[y * MAP_HORIZONTAL + x];
}

void map_move(size_t x1, size_t y1, size_t x2, size_t y2) {
  if (map_invalid_coord(x1, y1) || map_invalid_coord(x2, y2)) {
    return;
  }
  map_put(x2, y2, map_get(x1, y1));
  map_put(x1, y1, ' ');
}

static bool map_invalid_coord(size_t x, size_t y) {
  return x < 0 && MAP_HORIZONTAL <= x && y < 0 && MAP_VERTICAL <= y;
}