If statement doesn't work, equal sign does not match operand

Im making a two player tic tac toe game and in my check valid move function i have an if statement to check whether or not a move has been put there but an error keeps popping up.

bool check_valid(int row , int column) {
        if (board[row - 1][column - 1] == 'x' || board[row - 1][column - 
1] == 'o')
            return true;
        else
            return false;

error : no operator "==" matches these operands