#include <stdio.h>
#include <iostream.h>

const int wins[8][3] = {{0,1,2},{3,4,5},{6,7,8},{0,3,6},{1,4,7},{2,5,8},
                        {0,4,8},{2,4,6}};


void initialize_board(char board[9])
{
   for (int i=0; i<9; ++i) 
       board[i] = ' ';
}

void print_board(char board[9])
{
   for (int i=0;i<9;i+=3) 
   {
      printf(" %c | %c | %c\n",board[i],board[i+1],board[i+2]);
      if (i <= 3)
         printf("---+---+---\n");
   }
}

// test for a draw

int draw(char board[])
{
   int i;
   for (i = 0; i < 9 && board[i] != ' '; ++i);
   return (i==9); 
}

// test for three-in-a-row

int three_in_a_row(char board[9], char piece)
{
   for (int i=0; i<8; ++i) 
   {
     if ((board[wins[i][0]] == piece) && (board[wins[i][1]] == piece) &&
						(board[wins[i][2]] == piece))
        return(1);
   }
   return 0;
}

// allow human (O) to make a move

void human_move(char board[9])
{
   int move;

   do 
   {
      fflush(stdin);
      printf("enter your move: ");
      scanf("%d", &move);
   } while (move < 0 || move > 8 || board[move] != ' ');
   board[move] = 'O';
}

// test for two-in-a-row with an empty piece in the third square

int two_in_a_row(char board[9], char piece)
{
   for (int i=0; i<8; ++i) 
   {
     if ((board[wins[i][0]] == piece) && (board[wins[i][1]] == piece) &&
						   (board[wins[i][2]] == ' '))
        return(wins[i][2]);
     if ((board[wins[i][1]] == piece) && (board[wins[i][2]] == piece) &&
						   (board[wins[i][0]] == ' '))
        return(wins[i][0]);
     if ((board[wins[i][0]] == piece) && (board[wins[i][2]] == piece) &&
						   (board[wins[i][1]] == ' '))
        return(wins[i][1]);
   }
   return -1;
}

// find an open corner square

int corner_square(char board[9])
{
   int i;

   for (i=0;i<=8; i+=2)
      if (board[i] == ' ')
	 return i;
   return -1;
}

// find any open square

int first_empty_square(char board[9])
{
   int i;
   for (i=0;i<9;++i)
      if (board[i] == ' ')
         return i;
   return -1;
}

// computer move strategy

void computer_move(char board[9])
{
   int move;

   if (board[4] == ' ') // move to center square if open
      move = 4;
   else 
   {
      // check for two-in-a-row for a win
      if ((move = two_in_a_row(board,'X')) < 0) 
      {
         // check for two-in-a-row for a block
	 if ((move = two_in_a_row(board, 'O')) < 0)  
	 {
	    // check for a corner square
	    if ((move = corner_square(board)) < 0)
	       move = first_empty_square(board); // take whatever square is left
	 }
      }
   }

   printf("I move to square %d\n", move);
   board[move] = 'X';
}

// Play the game of tic-tac-toe where the computer goes first.
// The computer is X, the human is O.

void main()
{
   char board[9];
   int game_over;

   initialize_board(board);
   do
   {
      computer_move(board);
      print_board(board);
      if (game_over = three_in_a_row(board,'X'))
	 printf("I WIN!\n");
      else if (game_over = draw(board))
	 printf("DRAW\n");
      else
      {
	 human_move(board);
	 if (three_in_a_row(board,'O'))
	 {
	    game_over = 1;
	    printf("YOU WIN!\n");
	 }
      }
   } while (!game_over);
}