Sarkurd 0 Junior Poster in Training

Hi
after some months learing basics of C++, today i started by creating a simple game
but i have problem two problems
1- checkwin() doesn't work properly
2- the code goes glitchy if i press Enter before choosing a block

sorry for my english

#include <iostream>

using namespace std;

char square[10] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };

void GameBoard();
int checkwin();

int main(){

    GameBoard();
    int choice, i;
    int player = 1;
    char mark;
    do{
        if (player == 1)
            mark = 'X';
        else
            mark = 'O';
        cout << "Player " << player << " Enter a number: ";
        cin >> choice;
        if (choice == 1 && square[1] == '1')
            square[1] = mark;
        else if (choice == 2 && square[2] == '2')
            square[2] = mark;
        else if (choice == 3 && square[3] == '3')
            square[3] = mark;
        else if (choice == 4 && square[4] == '4')
            square[4] = mark;
        else if (choice == 5 && square[5] == '5')
            square[5] = mark;
        else if (choice == 6 && square[6] == '6')
            square[6] = mark;
        else if (choice == 7 && square[7] == '7')
            square[7] = mark;
        else if (choice == 8 && square[8] == '8')
            square[8] = mark;
        else if (choice == 9 && square[9] == '9')
            square[9] = mark;
        else
        {
            cout << "This Block already taken!" << endl;
            player--;
        }
        if (player == 1)
            player++;
        else
            player--;
        system("cls");
        GameBoard();
        i = checkwin();
    } while (i=-1);

    if (i == 1){
        cout << "Player " << player << "is win!" << endl;
    }
    else{
        cout << "Draw!" << endl;
    }
    cin.ignore();
    cin.get();
    return 0;
}

int checkwin()
{
    if (square[1] == square[2] && square[2] == square[3])

        return 1;
    else if (square[4] == square[5] && square[5] == square[6])

        return 1;
    else if (square[7] == square[8] && square[8] == square[9])

        return 1;
    else if (square[1] == square[4] && square[4] == square[7])

        return 1;
    else if (square[2] == square[5] && square[5] == square[8])

        return 1;
    else if (square[3] == square[6] && square[6] == square[9])

        return 1;
    else if (square[1] == square[5] && square[5] == square[9])

        return 1;
    else if (square[3] == square[5] && square[5] == square[7])

        return 1;
    else if (square[1] != '1' && square[2] != '2' && square[3] != '3'
        && square[4] != '4' && square[5] != '5' && square[6] != '6'
        && square[7] != '7' && square[8] != '8' && square[9] != '9')

        return 0;
    else
        return -1;
}

void GameBoard(){
    cout << "         Tic Tac Toe         " << endl << endl;
    cout << "Player 1: X , Player 2: O" << endl;
    cout << "   | " << "  |   " << endl;
    cout << " " << square[1] << " | " << square[2] << " | " << square[3] << " " << endl;
    cout << "___ ___ ___" << endl;
    cout << "   | " << "  |   " << endl;
    cout << " " << square[4] << " | " << square[5] << " | " << square[6] << " " << endl;
    cout << "___ ___ ___" << endl;
    cout << "   | " << "  |   " << endl;
    cout << " " << square[7] << " | " << square[8] << " | " << square[9] << " " << endl;

}