/*
Beginning C, Third Edition
By Ivor Horton
ISBN: 1-59059-253-0
Published: Apr 2004
Publisher: apress
*/
#include <stdio.h>
#include <ctype.h>
#define SIZE 6 /* Board size - must be even */
/* Function prototypes */
void display(char board[][SIZE]);
int valid_moves(char board[][SIZE], int moves[][SIZE], char player);
void make_move(char board[][SIZE], int row, int col, char player);
void computer_move(char board[][SIZE], int moves[][SIZE], char player);
int best_move(char board[][SIZE], int moves[][SIZE], char player);
int get_score(char board[][SIZE], char player);
void main()
{
char board [SIZE][SIZE] = { 0 }; /* The board */
int moves[SIZE][SIZE] = { 0 }; /* Valid moves */
int row = 0; /* Board row index */
int col = 0; /* Board column index */
int no_of_games = 0; /* Number of games */
int no_of_moves = 0; /* Count of moves */
int invalid_moves = 0; /* Invalid move count */
int comp_score = 0; /* Computer score */
int user_score = 0; /* Player score */
char y = 0; /* Column letter */
int x = 0; /* Row number */
char again = 0; /* Replay choice input */
int player = 0; /* Player indicator */
printf("\nREVERSI\n\n");
printf("You can go first on the first game, then we will take turns.\n");
printf(" You will be white - (O)\n I will be black - (@).\n");
printf("Select a square for your move by typing a digit for the row\n "
"and a letter for the column with no spaces between.\n");
printf("\nGood luck! Press Enter to start.\n");
scanf("%c", &again);
/* Prompt for how to play - as before */
/* The main game loop */
do
{
/* On even games the player starts; */
/* on odd games the computer starts */
player = ++no_of_games % 2;
no_of_moves = 4; /* Starts with four counters */
/* Blank all the board squares */
for(row = 0; row < SIZE; row++)
for(col = 0; col < SIZE; col++)
board[row][col] = ' ';
/* Place the initial four counters in the center */
board[SIZE/2 - 1][SIZE/2 - 1] = board[SIZE/2][SIZE/2] = 'O';
board[SIZE/2 - 1][SIZE/2] = board[SIZE/2][SIZE/2 - 1] = '@';
/* The game play loop */
do
{
display(board); /* Display the board */
if(player++ % 2)
{ /* It is the player's turn */
if(valid_moves(board, moves, 'O'))
{
/* Read player moves until a valid move is entered */
for(;;)
{
fflush(stdin); /* Flush the keyboard buffer */
printf("Please enter your move (row column): ");
scanf("%d%c", &x, &y); /* Read input */
y = tolower(y) - 'a'; /* Convert to column index */
x--; /* Convert to row index */
if( x>=0 && y>=0 && x<SIZE && y<SIZE && moves[x][y])
{
make_move(board, x, y, 'O');
no_of_moves++; /* Increment move count */
break;
}
else
printf("Not a valid move, try again.\n");
}
}
else /* No valid moves */
if(++invalid_moves<2)
{
fflush(stdin);
printf("\nYou have to pass, press return");
scanf("%c", &again);
}
else
printf("\nNeither of us can go, so the game is over.\n");
}
else
{ /* It is the computer's turn */
if(valid_moves(board, moves, '@')) /* Check for valid moves */
{
invalid_moves = 0; /* Reset invalid count */
computer_move(board, moves, '@');
no_of_moves++; /* Increment move count */
}
else
{
if(++invalid_moves<2)
printf("\nI have to pass, your go\n"); /* No valid move */
else
printf("\nNeither of us can go, so the game is over.\n");
}
}
}while(no_of_moves < SIZE*SIZE && invalid_moves<2);
/* Game is over */
display(board); /* Show final board */
/* Get final scores and display them */
comp_score = user_score = 0;
for(row = 0; row < SIZE; row++)
for(col = 0; col < SIZE; col++)
{
comp_score += board[row][col] == '@';
user_score += board[row][col] == 'O';
}
printf("The final score is:\n");
printf("Computer %d\n User %d\n\n", comp_score, user_score);
fflush(stdin); /* Flush the input buffer */
printf("Do you want to play again (y/n): ");
scanf("%c", &again); /* Get y or n */
}while(tolower(again) == 'y'); /* Go again on y */
printf("\nGoodbye\n");
}
/***********************************************
* Function to display the board in it's *
* current state with row numbers and column *
* letters to identify squares. *
* Parameter is the board array. *
***********************************************/
void display(char board[][SIZE])
{
int row = 0; /* Row index */
int col = 0; /* Column index */
char col_label = 'a'; /* Column label */
printf("\n "); /* Start top line */
for(col = 0 ; col<SIZE ;col++)
printf(" %c", col_label+col); /* Display the top line */
printf("\n"); /* End the top line */
/* Display the intermediate rows */
for(row = 0; row < SIZE; row++)
{
printf(" +");
for(col = 0; col<SIZE; col++)
printf("---+");
printf("\n%2d|",row + 1);
for(col = 0; col<SIZE; col++)
printf(" %c |", board[row][col]); /* Display counters in row */
printf("\n");
}
printf(" +"); /* Start the bottom line */
for(col = 0 ; col<SIZE ;col++)
printf("---+"); /* Display the bottom line */
printf("\n"); /* End the bottom line */
}
/***********************************************
/* Calculates which squares are valid moves *
* for player. Valid moves are recorded in the *
* moves array - 1 indicates a valid move, *
* 0 indicates an invalid move. *
* First parameter is the board array *
* Second parameter is the moves array *
* Third parameter identifies the player *
* to make the move. *
* Returns valid move count. *
***********************************************/
int valid_moves(char board[][SIZE], int moves[][SIZE], char player)
{
int rowdelta = 0; /* Row increment around a square */
int coldelta = 0; /* Column increment around a square */
int row = 0; /* Row index */
int col = 0; /* Column index */
int x = 0; /* Row index when searching */
int y = 0; /* Column index when searching */
int no_of_moves = 0; /* Number of valid moves */
/* Set the opponent */
char opponent = (player == 'O')? '@' : 'O';
/* Initialize moves array to zero */
for(row = 0; row < SIZE; row++)
for(col = 0; col < SIZE; col++)
moves[row][col] = 0;
/* Find squares for valid moves. */
/* A valid move must be on a blank square and must enclose */
/* at least one opponent square between two player squares */
for(row = 0; row < SIZE; row++)
for(col = 0; col < SIZE; col++)
{
if(board[row][col] != ' ') /* Is it a blank square? */
continue; /* No - so on to the next */
/* Check all the squares around the blank square */
/* for the opponents counter */
for(rowdelta = -1; rowdelta <= 1; rowdelta++)
for(coldelta = -1; coldelta <= 1; coldelta++)
{
/* Don't check outside the array, or the current square */
if(row + rowdelta < 0 || row + rowdelta >= SIZE ||
col + coldelta < 0 || col + coldelta >= SIZE ||
(rowdelta==0 && coldelta==0))
continue;
/* Now check the square */
if(board[row + rowdelta][col + coldelta] == opponent)
{
/* If we find the opponent, move in the delta direction */
/* over opponent counters searching for a player counter */
x = row + rowdelta; /* Move to */
y = col + coldelta; /* opponent square */
/* Look for a player square in the delta direction */
for(;;)
{
x += rowdelta; /* Go to next square */
y += coldelta; /* in delta direction*/
/* If we move outside the array, give up */
if(x < 0 || x >= SIZE || y < 0 || y >= SIZE)
break;
/* If we find a blank square, give up */
if(board[x][y] == ' ')
break;
/* If the square has a player counter */
/* then we have a valid move */
if(board[x][y] == player)
{
moves[row][col] = 1; /* Mark as valid */
no_of_moves++; /* Increase valid moves count */
break; /* Go check another square */
}
}
}
}
}
return no_of_moves;
}
/************
* Finds the best move for the computer. This is the move for *
* which the opponent's best possible move score is a minimum. *
* First parameter is the board array. *
* Second parameter is the moves array containing valid moves. *
* Third parameter identifies the computer. *
************/
void computer_move(char board[][SIZE], int moves[][SIZE], char player)
{
int row = 0; /* Row index */
int col = 0; /* Column index */
int best_row = 0; /* Best row index */
int best_col = 0; /* Best column index */
int i = 0; /* Loop index */
int j = 0; /* Loop index */
int new_score = 0; /* Score for current move */
int score = 100; /* Minimum opponent score */
char temp_board[SIZE][SIZE]; /* Local copy of board */
int temp_moves[SIZE][SIZE]; /* Local valid moves array */
char opponent = (player == 'O')? '@' : 'O'; /* Identify opponent */
/* Go through all valid moves */
for(row = 0; row < SIZE; row++)
for(col = 0; col < SIZE; col++)
{
if(moves[row][col] == 0)
continue;
/* First make copies of the board and moves arrays */
for(i = 0; i < SIZE; i++)
for(j = 0; j < SIZE; j++)
temp_board[i][j] = board[i][j];
/* Now make this move on the temporary board */
make_move(temp_board, row, col, player);
/* find valid moves for the opponent after this move */
valid_moves(temp_board, temp_moves, opponent);
/* Now find the score for the opponents best move */
new_score = best_move(temp_board, temp_moves, opponent);
if(new_score<score) /* Is it worse? */
{ /* Yes, so save this move */
score = new_score; /* Record new lowest opponent score */
best_row = row; /* Record best move row */
best_col = col; /* and column */
}
}
/* Make the best move */
make_move(board, best_row, best_col, player);
}
/************
* Calculates the score for the current board position for the *
* player. player counters score +1, opponent counters score -1 *
* First parameter is the board array *
* Second parameter identifies the player *
* Return value is the score. *
************/
int get_score(char board[][SIZE], char player)
{
int score = 0; /* Score for current position */
int row = 0; /* Row index */
int col = 0; /* Column index */
char opponent = player == 'O' ? '@' : 'O'; /* Identify opponent */
/* Check all board squares */
for(row = 0; row < SIZE; row++)
for(col = 0; col < SIZE; col++)
{
score -= board[row][col] == opponent; /* Decrement for opponent */
score += board[row][col] == player; /* Increment for player */
}
return score;
}
/************
* Calculates the score for the best move out of the valid moves *
* for player in the current position. *
* First parameter is the board array *
* Second parameter is the moves array defining valid moves. *
* Third parameter identifies the player *
* The score for the best move is returned *
************/
int best_move(char board[][SIZE], int moves[][SIZE], char player)
{
int row = 0; /* Row index */
int col = 0; /* Column index */
int i = 0; /* Loop index */
int j = 0; /* Loop index */
char opponent = player=='O'?'@':'O'; /* Identify opponent */
char new_board[SIZE][SIZE] = { 0 }; /* Local copy of board */
int score = 0; /* Best score */
int new_score = 0; /* Score for current move */
/* Check all valid moves to find the best */
for(row = 0 ; row<SIZE ; row++)
for(col = 0 ; col<SIZE ; col++)
{
if(!moves[row][col]) /* Not a valid move? */
continue; /* Go to the next */
/* Copy the board */
for(i = 0 ; i<SIZE ; i++)
for(j = 0 ; j<SIZE ; j++)
new_board[i][j] = board[i][j];
/* Make move on the board copy */
make_move(new_board, row, col, player);
/* Get score for move */
new_score = get_score(new_board, player);
if(score<new_score) /* Is it better? */
score = new_score; /* Yes, save it as best score */
}
return score; /* Return best score */
}
/*************
* Makes a move. This places the counter on a square,and reverses *
* all the opponent's counters affected by the move. *
* First parameter is the board array. *
* Second and third parameters are the row and column indices. *
* Fourth parameter identifies the player. *
*************/
void make_move(char board[][SIZE], int row, int col, char player)
{
int rowdelta = 0; /* Row increment */
int coldelta = 0; /* Column increment */
int x = 0; /* Row index for searching */
int y = 0; /* Column index for searching */
char opponent = (player == 'O')? '@' : 'O'; /* Identify opponent */
board[row][col] = player; /* Place the player counter */
/* Check all the squares around this square */
/* for the opponents counter */
for(rowdelta = -1; rowdelta <= 1; rowdelta++)
for(coldelta = -1; coldelta <= 1; coldelta++)
{
/* Don't check off the board, or the current square */
if(row + rowdelta < 0 || row + rowdelta >= SIZE ||
col + coldelta < 0 || col + coldelta >= SIZE ||
(rowdelta==0 && coldelta== 0))
continue;
/* Now check the square */
if(board[row + rowdelta][col + coldelta] == opponent)
{
/* If we find the opponent, search in the same direction */
/* for a player counter */
x = row + rowdelta; /* Move to opponent */
y = col + coldelta; /* square */
for(;;)
{
x += rowdelta; /* Move to the */
y += coldelta; /* next square */
/* If we are off the board give up */
if(x < 0 || x >= SIZE || y < 0 || y >= SIZE)
break;
/* If the square is blank give up */
if(board[x][y] == ' ')
break;
/* If we find the player counter, go backwards from here */
/* changing all the opponents counters to player */
if(board[x][y] == player)
{
while(board[x-=rowdelta][y-=coldelta]==opponent) /* Opponent? */
board[x][y] = player; /* Yes, change it */
break; /* We are done */
}
}
}
}
}
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