Players don't change

Ok I have a Tic Tac Toe game, and I just changed the structure of it and it won't alternate between players. It switches in the function, but the player doesn't change when the loop starts over. Here are the three functions that will be needed:

Code:

---

void GameMain() {
        GameInit();
        do {
                ShowGrid();
                GetInput(player);
                Write2Grid(choice, player);
        }while (true);
}

char GetInput(int player) { 
                switch(player) {       
                        case 1:
                        cout << "It's X's turn. " << endl;
                        cin >> choice;
                        break;
                case 2:
                        cout << "It's O's turn. " << endl;
                        cin >> choice;
                        break;
                default:
                        cout << "Error! Program will now terminate.";
                        getch();
                        exit(0);
                        break;
        }
        return choice;
}

void Write2Grid(int choice, int player) {       
        if (choice < 1 || choice > 9) {
                cout << "Select a number that's on the board." << endl;
                getch();
        }
        char xo;                                       
        xo = (player == 1) ? 'X' : 'O';
        int c = 2 - (choice-1)/3;
        int d = (choice-1)%3;
        if ( (Grid[c][d] == 'X') || (Grid[c][d] == 'O') ) {
                cout << "Spot has already been taken! Select another spot." << endl;
                getch();
        }
        else {
                Grid[c][d] = xo;
                if (CheckWin() == true) {
                        system("cls");
                        ShowGrid();
                        cout << "Congradulations, "<< xo << " has won!" << endl;
                        getch();
                        PlayAgain();
                }
                else {
                        player = (player == 1) ? 2 : 1;
                }
        }
}

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>>void Write2Grid(int choice, int player)
Change that to
void Write2Grid(int choice, int &player)

Otherwise, the value of player will only be modified within the Write2Grid function, and the player will stay the same.

ok thanks, i have to understand pointers better so things like this won't happen again.