Thread: Minimax algorithm not behaving properly

I have been learning to program for a couple months now and decided to take a shot at tic-tac-toe and an AI to accompany it. From what I've seen elsewhere, everything in the ai() and minimax() functions should be working properly, however I have noted that the AI tends to miss wins and assume it is a draw in won positions.

Code:

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

char board[3][3] = {{' ',' ',' '},{' ',' ',' '},{' ',' ',' '}};
int drawBoard();
int turn();
int turns();
int winner();
int ai(char current[3][3]);
int minimax(char test[3][3], int player);

int main()
{
    int players;
    
    printf("How many players? (1 - 2): ");
    scanf("%d", &players);
    
    if(players == 1)
    {
        do
        {
             system("clear");
            drawBoard();
            turn();
            if(winner(board) != 0 && winner(board) != 1 && winner(board) != -1)
            {
            ai(board);
            }
        }
        while(winner(board) != 1 && winner(board) != -1 && winner(board) != 0);
    }
    else if(players == 2)
    {
        do
        {
            system("clear");
            drawBoard();
            turns();
        }
        while(winner(board) != 1 && winner(board) != -1 && winner(board) != 0);
    }
    
    system("clear");
    drawBoard();
    if(winner(board) != 0)
    {
    printf("Game Over!\nWinner is player %d\n", (winner(board)+3)/2);
    }
    else
    {
    printf("It is a draw!\n");
    }
    return 0;
}

int drawBoard()
{
    for (int i = 1; i < 12; i++)
    {
        if(i % 4 == 0)
        {
            printf("---------------------\n");
        }
        else if(i % 2 == 0)
        {
            printf("  %c   |   %c   |   %c  \n", board[(i-2)/4][0], board [(i-2)/4][1],                  
            board[(i-2)/4][2]);
        }
        else
        {
            printf("      |       |      \n");
        }
    }
}

int turn()
{
    int row, col;
    
    printf("Select a row: ");
    scanf("%d", &row);
    printf("Select a column: ");
    scanf("%d", &col);

    if(board[row-1][col-1] != ' ')
    {
        printf("Please try again!\n");
        turn();
        return 0;
    }

    board[row-1][col-1] = 'X';
}

int turns()
{
    static int player = 1;
    int row, col;
    
    printf("Player %d select a row: ", player);
    scanf("%d", &row);
    printf("Player %d select a column: ", player);
    scanf("%d", &col);

    if(board[row-1][col-1] != ' ')
    {
        printf("Please try again!\n");
        turns();
        return 0;
    }

    if(player == 1)
    {
        board[row-1][col-1] = 'X';
        player = 2;
    }
    else
    {
        board[row-1][col-1] = 'O';
        player = 1;
    }
}

signed int winner(char check[3][3])
{
    int i, j, temp, total = 0;

    for(i = 0; i < 3; i++)
    {
        
        if(check[i][0] == check[i][1] && check[i][0] == check[i][2] && check[i][0] != ' ')
        {
            temp = (int)check[i][0];
            if(temp == 88)
            {
                return -1;
            }
            else
            {
                return 1;
            }
        }
        if(check[0][i] == check[1][i] && check[0][i] == check[2][i] && check[0][i] != ' ')
        {
            temp = (int)check[0][i];
            if(temp == 88)
            {
                return -1;
            }
            else
            {
                return 1;
            }
        }
    }
    if(check[0][0] == check[1][1] && check[0][0] == check[2][2] && check[0][0] != ' ')
    {
        temp = (int)check[0][0];
        if(temp == 88)
        {
            return -1;
        }
        else
        {
            return 1;
        }
    }
    if(check[2][0] == check[1][1] && check[2][0] == check[0][2] && check[2][0] != ' ')
    {
        temp = (int)check[2][0];
        if(temp == 88)
        {
            return -1;
        }
        else
        {
            return 1;
        }
    }
    
    for(i = 0; i < 3; i++){
    for(j = 0; j < 3; j++){
    temp = (int)check[i][j];
    if(check[i][j] != 32)
    {
        total += 1;
    }}}
    if(total == 9)
    {
    return 0;
    }
}

int ai(char current[3][3])
{
    signed int score, bestScore = -1000;
    int bestMove[2];

    for(int i = 0; i < 3; i++){
    for(int j = 0; j < 3; j++){
        if((int)current[i][j] == 32)
        {
            current[i][j] = 'O';
            score = minimax(current, 1);
            current[i][j] = ' ';
            if(score > bestScore)
            {
                bestScore = score;
                bestMove[0] = i;
                bestMove[1] = j;
            }
        }
    }
    }
    board[bestMove[0]][bestMove[1]] = 'O';
}

int minimax(char test[3][3], int player)
{
    int i, j, score;
    
    if(winner(test) == 0 || winner(test) == 1 || winner(test) == -1)
    {
        return winner(test);
    }
    if(player == 2)
    {
        signed int bestScore = -1000;
        for(int i = 0; i < 3; i++){
        for(int j = 0; j < 3; j++){
            if((int)test[i][j] == 32)
            {
                test[i][j] = 'O';
                drawBoard();
                score = minimax(test, 1);
                test[i][j] = ' ';
            
                if(score > bestScore)
                {
                    bestScore = score;
                }
            }
        }}
        return bestScore;
    }
    else
    {
        signed int bestScore = 1000;
        for(int i = 0; i < 3; i++){
        for(int j = 0; j < 3; j++){
            if((int)test[i][j] == 32)
            {
                test[i][j] = 'X';
                drawBoard();
                score = minimax(test, 2);
                test[i][j] = ' ';
            
                if(score < bestScore)
                {
                    bestScore = score;
                }
            }
        }}
        return bestScore;
    }
}

I have looked through this so many times and can not for the life of me find an error. Thanks in advance!

It is worth noting that the algorithm will never lose. When X is placed in the centre of the board, it will always pick a corner (whether or not that is thanks to the minimax is debatable), and it will always pick the centre if any other move is played. It just seems to ignore wins for some reason...