A tic tac toe ai.

tic-ai.c

#include <stdio.h>
#include <string.h>

int win(int board[9]) {
    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}};
    for(int i = 0; i < 8; ++i) {
        if(board[wins[i][0]] != 0 &&
           board[wins[i][0]] == board[wins[i][1]] &&
           board[wins[i][0]] == board[wins[i][2]])
            return board[wins[i][2]];
    }
    return 0;
}

char getHuman(int board[9], int i) {
    switch (board[i]) {
        case -1:
            return 'X';
        case 1:
            return 'O';
        case 0:
            return '0' + i;
    }
    return 0;
}

void copyBoard(int board[9], int dest[9]) {
    for (int i = 0; i < 9; i++)
        dest[i] = board[i];
}

void printBoard(int board[9]) {
    printf("\n%c  %c  %c\n",getHuman(board,0),getHuman(board,1),getHuman(board,2));
    printf("%c  %c  %c\n",getHuman(board,3),getHuman(board,4),getHuman(board,5));
    printf("%c  %c  %c\n\n",getHuman(board,6),getHuman(board,7),getHuman(board,8));
}

void playerMove(int board[9]) {
    printf("move (0 - 8)? ");
    int move;

    while (!scanf("%d",&move)) {
        scanf("%*[^\n]");
        printBoard(board);
        printf("huh?\n");
        printf("move (0 - 8)? ");
    }

    if (move > 8 || move < 0) {
        printBoard(board);
        printf("nice try.\n");
        playerMove(board);
    } else if (board[move] != 0) {
        printBoard(board);
        printf("cheater.\n");
        playerMove(board);
    } else
        board[move] = -1;
}

int minmax(int board[9], int from) {
    if (win(board) != 0) return win(board)*from; //if return 1 if fails do -1
    int move = -1;
    int score = -2;
    int temp[9];

    for(int i = 0; i < 9; i++) { //for all moves
        if(board[i] == 0) { //if legal
            copyBoard(board,temp);
            temp[i] = from; //try move
            int tempScore = -minmax(temp, -from); //minmax from player
            if(tempScore > score) {
                score = tempScore;
                move = i;
            }
        }
    }

    if (move == -1)
        return 0;
    return score;
}

void computerMove(int board[9]) {
    int move = -1;
    int score = -2;
    int temp[9];
    for(int i = 0; i < 9; i++) { //for all moves
        if(board[i] == 0) { //if legal
            copyBoard(board,temp);
            temp[i] = 1; //try move
            int tempScore = -minmax(temp, -1); //minmax from player
            if(tempScore > score) {
                score = tempScore;
                move = i;
            }
        }
    }
    if (move != -1)
        board[move] = 1; //move if found move
}

int main() {
    int board[9] = {0,0,0,0,0,0,0,0}; //ai is 1 player is -1
    printf("first(1) or second(2): ");
    int player=0;
    scanf("%d",&player);

    for (int turn = 0; turn < 9; turn++) {
        switch (win(board)) {
            case 1:
                printBoard(board);
                printf("you loose.\n");
                return 0;
                break;
            case -1:
                printBoard(board);
                printf("you win. :)\n");
                return 0;
                break;
        }
        if (player == 1) {
            printBoard(board);
            playerMove(board);
            player = 2;
        } else {
            computerMove(board);
            player = 1;
        }
    }
    printf("draw.\n\
      /|_____|\\  \n\
   __|  o   o  |__\n\
   __|    v    |__\n\
      \\_______/ \n\
    ");
    return 0;
}