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tictactoe

This example is a Tic Tac Toe game for two playings taking turns. Before each turn, the current state of the game map is printed. Players then enter turns by giving the coordinates (A1, B3, C2, ...) where they want to put their next mark. The goal is to place three marks adjacent to each other. The game ends in a draw when all map squares have been marked without either player placing three marks in a row.

Source code

/*
 * convert field contents to string (0 = empty, 1 = X, 2 = O)
 */
string str_field(int field)
{
  chars = mkarray(" ", "X", "O");
  return chars[field];
}

/*
 * print game map (two-dimensional 3x3 array)
 */
void print_map(array map)
{
  print("\n   A B C\n");
  for (i = 0; i < 3; i++) {
    print("  +-+-+-+\n", i + 1, " |");
    for (j = 0; j < 3; j++) {
      print(str_field(map[i][j]), "|");
    }
    print("\n");
  }
  print("  +-+-+-+\n");
}

/*
 * get winner if any (0 = none, 1 = X, 2 = O)
 */
int get_winner(array a)
{
  for (i = 0; i < 3; i++) {
    if (a[i][0] && a[i][0] == a[i][1] && a[i][1] == a[i][2]) return a[i][0];
    if (a[0][i] && a[0][i] == a[1][i] && a[1][i] == a[2][i]) return a[0][i];
  }

  if (a[0][0] && a[0][0] == a[1][1] && a[1][1] == a[2][2]) return a[0][0];
  if (a[0][2] && a[0][2] == a[1][1] && a[1][1] == a[2][0]) return a[0][2];
  
  return 0;
}

/*
 * check for draw (all fields non-empty)
 */
bool is_draw(array map)
{
  for (i = 0; i < 3; i++) {
    for (j = 0; j < 3; j++) {
      if (map[i][j] == 0) return false;
    }
  }
  return true;
}

/*
 * initial game map (all fields empty)
 */
map = mkarray(mkarray(0, 0, 0), mkarray(0, 0, 0), mkarray(0, 0, 0));

/*
 * play the game
 */
turn = 0;
for (;;) {
  print_map(map);

  winner = get_winner(map);
  if (winner > 0) {
    print("\nPlayer ", str_field(winner), " has won!\n");
    break;
  }

  if (is_draw(map)) {
    print("\nThe game ends in a draw!\n");
    break;
  }

  print("Player ", str_field(turn % 2 + 1), ", your move? ");
  reply = fgets(stdin);

  x = toupper(substr(reply, 0, 1));
  x = ord(x) - ord("A");

  y = substr(reply, 1, 1);
  y = ord(y) - ord("1");

  if (x < 0 || x > 2 || y < 0 || y > 2) {
    print("Impossible move, try again.\n");
    continue;
  }

  if (map[y][x] != 0) {
    print("Already occupied, try again.\n");
    continue;
  }

  map[y][x] = (turn % 2) + 1;

  ++turn;
}