=============
石取りゲーム2
=============

.. code-block:: c

  #include <stdio.h>
  #include <stdlib.h>

  int main()
  {
      int i, max, n, x, f[21], r, my_turn;

      f[1] = f[2] = 1;
      for (i = 3; i <= 20; i++) f[i] = f[i - 1] + f[i - 2];

      printf("石の数 (2..10000)? ");
      scanf("%d", &n);
      if (n < 2 || n > 10000) return EXIT_FAILURE;

      max = n - 1;

      for (my_turn = 1; n != 0; my_turn ^= 1) {
          printf("%d 個まで取れます.\n", max);
          if (my_turn) {
              x = n;
              for (i = 20; x != f[i]; i--) {
                  if (x > f[i]) {
                      x -= f[i];
                  }
              }
              if (x > max) x = 1;
              printf("私は %d 個の石を取ります.\n", x);
          } else do {
              printf("何個取りますか? ");
              r = scanf("%d", &x);
              scanf("%*[^\n]");
          } while (r != 1 || x < 1 || x > max);
          n -= x;
          max = 2 * x;
          if (max > n) max = n;
          printf("残りは %d 個です.\n", n);
      }

      if (my_turn) {
          printf("あなたの勝ちです!\n");
      } else {
          printf("私の勝ちです!\n");
      }

      return EXIT_SUCCESS;
  }