converting int stored in array to char?

Doing another exercise on array, making another tic tac toe game, but now with varied board size. So I can't use board with char type.
Unless there's another way to show that the square is marked with O and X, I want to know how to convert int values stored in array into a char.

Code:

#include <iostream>
#include <string>


using namespace std;


void show_board(int board[][6],int board_size);
int game_start(int board[][6], string player[]);
int select_board(int board[][6]);


void player_names(string player[])
{   string player1,player2;
    std::cout << "Player 1's name: ";
    std::getline(cin, player1);
    std::cout<<endl;
    std::cout << "Player 2's name: ";
    std::getline(cin, player2);
    std::cout <<endl;


    player[0]= player1;
    player[1]= player2;


}


int game_start(int board[][6], string player[],int board_size)
{
    bool gameover = false;
    int turn =0; //0-'X', 1-'O'
    int mark;


    do{


        show_board(board,board_size);


        std::cout << player[0]<< "'s turn.\n";
        std::cin>>mark;


        for (int row=0;row<board_size;row++)
        {
            for(int column=0;column<board_size;column++)
            {
                if(board[row][column] == mark && turn == 0 ){


                   


                }
                else if(board[row][column] == mark && turn == 1){


                     
                }
            }
        }










    }
    while(!gameover);
}




void show_board(int board[][6],int board_size)
{


    for (int row=0;row<board_size;row++)
    {
         for(int column=0;column<board_size;column++)
        {
             if(board_size == 5){
                if(board[row][column] > 24){
                board[row][column] = board[row][column] - 4;}
                else if (board[row][column] > 18){
                board[row][column] = board[row][column] - 3;}
                else if (board[row][column] > 12){
                board[row][column] = board[row][column] - 2;}
                else if (board[row][column] > 6){
                board[row][column] = board[row][column] - 1;}
             }
             else if(board_size == 4){
                 if(board[row][column] > 18){
                board[row][column] = board[row][column] - 6;}
                else if (board[row][column] > 12){
                board[row][column] = board[row][column] - 4;}
                else if (board[row][column] > 6){
                board[row][column] = board[row][column] - 2;}


             }


             if (board[row][column] < 10){
             std::cout << " ";}






            std::cout << board[row][column] << " ";
        }
        std::cout << endl;
    }
}


int select_board(int board[][6])
{
    std::cout << "Select the size of board: \n";
    std::cout << " 4x4 - press 4.\n";
    std::cout << " 5x5 - press 5.\n";
    std::cout << " 6x6 - press 6.\n";
    int board_size;
    std::cin >> board_size;


    return board_size;
}
int main()
{
    int board[6][6] = { {1,2,3,4,5,6},
                        {7,8,9,10,11,12} ,
                        {13,14,15,16,17,18},
                        {19,20,21,22,23,24},
                        {25,26,27,28,29,30},
                        {31,32,33,34,35,36}};
    string player[2];
    player_names(player);
    int board_size = select_board(board);


    game_start(board,player,board_size);
}

ahh something i overlook the board too =.=