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ttt (single player Tic Tac Toe)

This example is a variant of Tic Tac Toe for a single player match against the computer. The rules should be clear. The best you can hope for is a draw.

Source code

// TicTacToe - Copyright 1997, 2006 J.L. Bezemer
// You can redistribute this file and/or modify it under
// the terms of the GNU General Public License

int enter () {
  return ((int) (fgets (stdin)));
}

convert = mkarray (0, 1, 2, 5, 8, 7, 6, 3, 4);
board   = mkarray (0, 0, 0, 0, 0, 0, 0, 0, 0);

void box (int x) {
  if (board [x]) print (board [x] == 1 ? "X " : "0 ");
  else print ("  ");
}

void display () {
  print ("\n");
  for (x = 0; x < 9; x++) {
     if (x) print (x % 3 ? "| " : "\n---------\n");
     box (x);
   }
   print ("\n");
}

void play (int m, int p) {
  if (m < 1) m = 1; if (m > 9) m = 9;  // clip values
  c = convert [m - 1];                 // get array address
  if (! board [c]) board [c] = p;      // set, if not occupied
}

void X (int c) {
  play (c, 1);
  display ();
}

void O (int p) {
  play (p, 2);
}

int fnM (int a, int b) {
  return ((((a + b) - 1) % 8) + 1);
}

int Player (int c) {
  X (c);                               // computers move
  print (" \n123\n894\n765 Your move: "); p = enter ();
  O (p); return (p);                   // my move
}

void EndGame (int m) {
    X (m);
    print ("\nYou lose.\n");
    exit (0);
}

void FirstMove (int f, int c) {
  if ((f % 2) == 0) EndGame (fnM (7, c));
}

int Moves (int m, int p) {
  c = fnM (m, p); p = Player (c); t = fnM (4, c);
  if (p != t) EndGame (t);
  return (c);
}

void TicTacToe () {
  f = Player (9);
  c = Moves (1, f);
  c = Moves (2, c);
  FirstMove (f, c);
  c = Moves (3, c);
  
  X (fnM (6, c)); print ("\nIt's a draw.\n");
}

TicTacToe ();