C: Referencing 2D array through multiple functions-CodePudding

I've been trying to make a tic tac toe game with the miniMax algorithm, but have run into a problem with accessing the array at the miniMax function: if (checkGameOver(board[3][3]) != 0); and the others.

giving the error:

incompatible integer to pointer conversion passing 'char' to parameter of type 'char *'; take the address with & [-Wint-conversion]

Pretty new to C, but I think I've messed up the referencing of the array somewhere.

int miniMax(char (*board)[3], int player)
{
    if (checkGameOver(board[3][3]) != 0)
    {
        if (checkGameOver(board[3][3]) == 1)
        {
            if (whichPlayer(-1 * (player)) == 1)
            {
                return MIN;
            }
            else if (whichPlayer(-1 * (player)) == -1)
            {
                return MAX;
            }
        }
        else if (checkGameOver(board[3][3]) == 2)
        {
            return 0;
        }
        else{exit(EXIT_FAILURE);}
}
}

void bestMove(char (*board)[3], int player, int *ptrRow, int *ptrCol)
{
    int bestMove[2] = {-1};
    int minEval = MIN;

    // code. Runs through all possible moves, and returns the best move
    for (int i = 0; i < 3;   i)
    {
        for (int j = 0; j < 3;   j)
        {
            board[i][j] = whichPlayer(player);
            int evalPos = miniMax(board, -1 * player);
            if (evalPos >= minEval)
            {
                minEval = evalPos;
                bestMove[0] = i;
                bestMove[1] = j;
            }
        }
    }
    // pointer to address of array in main func
    *ptrRow = bestMove[0];
    *ptrCol = bestMove[1];
}


int main()
{
    // 2D array
    char board[3][3] = {{'_', '_', '_'},
                        {'_', '_', '_'},
                        {'_', '_', '_'}};

    currentPlayer = 1;


    While (1)
    {

        char copyBoard[3][3] = {{'_'}, {'_'}, {'_'}};
        for (int i = 0; i < 3;   i)
        {
            for (int j = 0; j < 3;   j)
            {
                 copyBoard[i][j] = board[i][j];
            }
        }

        if (currentPlayer == 1)
        {
            int move[2] = {-1};
            bestMove(copyBoard, currentPlayer, &move[0], &move[1]);
            makeMove(board, move, currentPlayer);
            currentPlayer = currentPlayer * -1;
        }
}

CodePudding user response：

This error message

incompatible integer to pointer conversion passing 'char' to parameter of type 'char *'; take the address with & [-Wint-conversion]

is enough clear.

In statements like this

if (checkGameOver(board[3][3]) != 0)

the argument expression board[3][3] has the type char and moreover supplies a non-existent element of the array board because the valid range of indices is [0,3).

But the function expects an argument expression of the type char * that is a pointer.

So such if statements do not make sense.

CodePudding user response：

To fix the error, pass by reference instead of value, so

if (checkGameOver(board[3][3]) != 0)

becomes

if (checkGameOver(&board[3][3]) != 0)

this will pass a pointer to a char instead of a char. Assuming the function signature takes a char *, they need to match.

Vlad is also right, declaring a board[3][3] means the indices are 0, 1, and 2, so passing board[3][3] is out of bounds.

Also, board[3][3] only passes a single board position, and assuming the checkGameOver function needs to check the full board for a tic-tac-toe, you need to pass a pointer to the full board instead of a single value.

So if you declare

char board[3][3];

and the function declaration is

int checkGameOver(char **board);

you can call it like this

int a = checkGameBoard(&board);