Migotające kreski w programie

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

string direction()
{
   
    int key = getch();
    key += getch();
    if( key == 296 ) return "up"; //gora
    else if( key == 304 ) return "down"; //dol
    else if( key == 299 ) return "left"; //lewo
    else if( key == 301 ) return "right"; //prawo
   
}

void idzdoxy( int x, int y )
{
    HANDLE hCon;
    COORD dwPos;
   
    dwPos.X = x;
    dwPos.Y = y;
   
    hCon = GetStdHandle( STD_OUTPUT_HANDLE );
    SetConsoleCursorPosition( hCon, dwPos );
}

void boardDraw( string board[ 30 ][ 30 ] )
{
   
    for( int i = 0; i < 30; i++ )
    {
        for( int j = 0; j < 30; j++ ) cout << board[ i ][ j ];
       
        cout << endl;
    }
   
}


void point( string board[ 30 ][ 30 ] )
{
    int x = rand() % 28 + 1;
    int y = rand() % 28 + 1;
    board[ x ][ y ] = "* ";
}

void snake( string board[ 30 ][ 30 ], string & direct, int & snakeCordX, int & snakeCordY, int & size, int XHistory[ 100000 ], int YHistory[ 100000 ], int & nmb, bool & pointExist )
{
    XHistory[ nmb ] = snakeCordX;
    YHistory[ nmb ] = snakeCordY;
    nmb++;
   
   
    if( direct == "up" )
    {
        snakeCordX--;
    }
    else if( direct == "down" )
    {
        snakeCordX++;
    }
    else if( direct == "left" )
    {
        snakeCordY--;
    }
    else if( direct == "right" )
    {
        snakeCordY++;
    }
    //get point
    if( board[ snakeCordX ][ snakeCordY ] == "* " )
    {
        size++;
        pointExist = 0;
    }
    //game over
    if( board[ snakeCordX ][ snakeCordY ] == "--" || board[ snakeCordX ][ snakeCordY ] == "|" || board[ snakeCordX ][ snakeCordY ] == "x " )
    {
       
        cout << "przegrales ;(";
        system( "pause" );
    }
    board[ snakeCordX ][ snakeCordY ] = "x ";
    board[ XHistory[ nmb - size ] ][ YHistory[ nmb - size ] ] = "  ";
   
}






int main()
{
   
    srand( time( NULL ) );
    string direct = "up";
    int snakeCordX = 15;
    int snakeCordY = 15;
    bool pointExist = 0;
    int nmb = 0;
    int size = 1;
    int XHistory[ 100000 ];
    int YHistory[ 100000 ];
    //tablica
    string board[ 30 ][ 30 ];
    for( int i = 0; i < 30; i++ )
    {
        for( int j = 0; j < 30; j++ ) board[ i ][ j ] = "  ";
       
        cout << endl;
    }
    //snake generator
   
    board[ snakeCordX ][ snakeCordY ] = "x ";
   
    //ramka
    for( int i = 0; i < 30; i++ ) board[ 0 ][ i ] = "--";
   
    for( int i = 0; i < 30; i++ ) board[ 29 ][ i ] = "--";
   
    for( int i = 0; i < 30; i++ ) board[ i ][ 0 ] = "|";
   
    for( int i = 0; i < 30; i++ ) board[ i ][ 29 ] = "|";
   
   
    cout << endl;
    cout << endl;
    for(;; )
    {
        //system("cls");
        idzdoxy( 0, 0 );
        boardDraw( board );
        if( kbhit() ) direct = direction();
       
        snake( board, direct, snakeCordX, snakeCordY, size, XHistory, YHistory, nmb, pointExist );
        if( !pointExist )
        {
            point( board );
            pointExist = 1;
        }
       
        Sleep( 100 );
    }
    getch();
    return 0;
}