Tic Tac Toe game (system("cls") function will only work on windows)

TicTacToe.cpp

#include <iostream>
#include <windows.h>
using namespace std;

char table[3][3]={'1','2','3','4','5','6','7','8','9'};
char player='X';


void draw()
{
    system("cls");
    cout<<endl<<"Tic-Tac-Toe"<<endl<<endl;
    for(int i=0;i<3;i++)
    {
        cout<<"| ";
        for(int j=0;j<3;j++)
        {
            cout<<table[i][j]<<" | ";
        }
        cout<<endl<<"-------------"<<endl;
    }
}

void input()
{
    int a;
    cout<<"player "<<player<<"'s turn"<<endl<<endl;
    cout<<"Choose a number: ";
    cin>>a;

    if(a == 1)
    {
        if(table[0][0] == '1')
            table[0][0] = player;
        else
        { 
            cout <<endl<<"Field already in use!" <<endl<<endl;
            input();
        }
    }
    else if(a == 2)
    {
        if(table[0][1] == '2')
            table[0][1] = player;
        else
        {
            cout <<endl<<"Field already in use!" <<endl<<endl;
            input();
        }
    }
    else if(a == 3)
    {
        if(table[0][2] == '3')
            table[0][2] = player;
        else
        {
                cout <<endl<<"Field already in use!" <<endl<<endl;
            input();
        }
    }
    else if(a == 4)
    {
        if(table[1][0] == '4')
            table[1][0] = player;
        else
        {
            cout <<endl<<"Field already in use!" <<endl<<endl;
            input();
        }
    }
    else if(a == 5)
    {
        if(table[1][1] == '5')
            table[1][1] = player;
        else
        {
            cout <<endl<<"Field already in use!" <<endl<<endl;
            input();
        }
    }
    else if(a == 6)
    {
        if(table[1][2] == '6')
            table[1][2] = player;
        else
        {
            cout <<endl<<"Field already in use!" <<endl<<endl;
            input();
        }
    }
    else if(a == 7)
    {
        if(table[2][0] == '7')
            table[2][0] = player;
        else
        {
            cout <<endl<<"Field already in use!" <<endl<<endl;
            input();
        }
    }
    else if(a == 8)
    {
        if(table[2][1] == '8')
            table[2][1] = player;
        else
        {
            cout <<endl<<"Field already in use!" <<endl<<endl;
            input();
        }
    }
    else if(a == 9)
    {
        if(table[2][2] == '9')
            table[2][2] = player;
        else
        {
            cout <<endl<<"Field already in use!" <<endl<<endl;
            input();
        }
    }
}

void playerswitch()
{
    if(player=='X')
    {    
        player='O';
    }    
    else
    {
        player='X';
    }
}

char logic()
{
    if(table[0][0]=='X' && table[0][1]=='X' && table[0][2]=='X')
        return 'X';
    else if(table[0][0]=='X' && table[1][0]=='X' && table[2][0]=='X')
        return 'X';
    else if(table[0][2]=='X' && table[1][2]=='X' && table[2][2]=='X')
        return 'X';
    else if(table[2][0]=='X' && table[2][1]=='X' && table[2][2]=='X')
        return 'X';
    else if(table[0][0]=='X' && table[1][1]=='X' && table[2][2]=='X')
        return 'X';
    else if(table[0][2]=='X' && table[1][1]=='X' && table[2][0]=='X')
        return 'X';


    else if(table[0][0]=='O' && table[0][1]=='O' && table[0][2]=='O')
        return 'O';
    else if(table[0][0]=='O' && table[1][0]=='O' && table[2][0]=='O')
        return 'O';
    else if(table[0][2]=='O' && table[1][2]=='O' && table[2][2]=='O')
        return 'O';
    else if(table[2][0]=='O' && table[2][1]=='O' && table[2][2]=='O')
        return 'O';
    else if(table[0][0]=='O' && table[1][1]=='O' && table[2][2]=='O')
        return 'O';
    else if(table[0][2]=='O' && table[1][1]=='O' && table[2][0]=='O')
       { return 'O';}
    return '/';
}

void startgame()
{   table[0][0]='1'; table[0][1]='2'; table[0][2]='3';
    table[1][0]='4'; table[1][1]='5'; table[1][2]='6';
    table[2][0]='7'; table[2][1]='8'; table[2][2]='9';
    string again;
    draw();
    while(true)
    {
        input();
        draw();
        playerswitch();
        if(logic()=='X')
        {
            cout<<"Player x won!"<<endl<<endl<<"Play again? ";
            cin>>again;

            if(again=="yes" || again=="y")
            {   
                startgame();
            }
            else if(again=="no" || again=="n")
            {
                exit(0);
            }
        }

        else if(logic()=='O')
        {
            cout<<"Player O won!"<<endl<<endl<<"Play again? ";
            cin>>again;
            cout<<endl;

            if(again=="yes" || again=="y")
            {   
                startgame();
            }
            else if(again=="no" || again=="n")
            { 
                exit(0);
            }
        }

        else if(table[0][0]!='1' && table[0][1]!='2' && table[0][2]!='3' &&
    table[1][0]!='4' && table[1][1]!='5' && table[1][2]!='6' &&
    table[2][0]!='7' && table[2][1]!='8' && table[2][2]!='9' && logic()!='O' && logic()!='X')
        {
            cout<<"It's a draw!"<<endl<<endl<<"Play again? ";
            cin>>again;
            cout<<endl;

            if(again=="yes" || again=="y")
            {
                startgame();
            }
            else if(again=="no" || again=="n")
            {
                exit(0);
            }
        }
    }
}



int main()
{
    startgame();
}