Help concerning a basic simple snake game

[XYTetris]

So, I was trying to create a simple snake game the other day.
The code has been written, but a few problems popped out and I don't quite understand why.

1. when the snake eats at least one fruit, the 'y' for replay option doesn't work (SOLVED)

2. the snake occasionally goes into wall even though it is supposed to be on the edge

3.The limitations of the grid don't seem to correspond to the (x,y) coordinates that I assigned. Meaning that in order to make the snake "die" when touching the grid, I couldn't when if( x == 0 || x == width -1 || y == 0 || y == height -1) The conditions that I have currently in the codes doesn't work.

4. after precisely 33 fruits, there is no more generation of fruit in the board

Also, if I wanted to make the game bigger (like, to make every character appear bigger), how should I do that?

#include <iostream>
#include <conio.h>
#include <string>
#include <Windows.h>
using namespace std;

char head;
char tail = 'o';
bool GameOver, pause;
bool paint = false;
const int width = 20;
const int height = 20;
int x, y, fruitX, fruitY, score;
int tailX[100], tailY[100];
int ntail;
enum Direction {Stop=0, Left, Right, Up, Down};
Direction dir;


void SetUp() {
	GameOver = false;
	dir = Stop;
	x = width / 2;
	y = height / 2;
	fruitX = rand() % width;
	fruitY = rand() % height;
	score = 0;
	head = '@';
	pause = false;
}

void Draw() {
	system("cls");
	for (int i = 0; i < width; i++)
	{
		cout << '#';
	}

	cout << "W(5), A(1), S(2), and D(3) to move, X to end and P to pause";
	cout << endl;
	for (int i = 0; i < height; i++)
	{
		for (int j = 0; j < width; j++)
		{
			if ((j == 0) || j == (width - 1))
			{
				cout << '#';
			}
			else if ((j == x) && (i == y))
			{
				cout << head;
			}
			else if ((j == fruitX) && (i == fruitY))
			{
				cout << 'F';
			}
			else
			{
				for (int k = 0; k < ntail; k++)
				{
					if (tailX[k] == j && tailY[k] == i)
					{
						cout << tail;
						paint = true;
					}
				}
				if (!paint){
					cout << ' ';
				}
				paint = false;
			}
		}
		cout << endl;
	}
	for (int i = 0; i < width; i++)
	{
		cout << '#';
	}
	cout << endl << "Score: " << score;
	if (pause)
	{
		cout << "        PAUSED";
	}
}

void Input() {
	if (_kbhit())
	{
		switch (cin.get())
		{
		case 'w': 
			dir = Up;
			break;
		case 'a':
			dir = Left;
			break;
		case 's':
			dir = Down;
			break;
		case 'd':
			dir = Right;
			break;
		case '5':
			dir = Up;
			break;
		case '1':
			dir = Left;
			break;
		case '2':
			dir = Down;
			break;
		case '3':
			dir = Right;
			break;
		case 'p':
			if (!pause)
			{
				pause = true;
			}
			else
			{
				pause = false;
			}
			break;
		case 'x':
			GameOver = true;
			break;
		}
	}
}

void Logic() {

	int prevX = tailX[0];
	int prevY = tailY[0];
	int prev2X, prev2Y;
	tailX[0] = x;
	tailY[0] = y;

	for (int i = 1; i < ntail; i++)
	{
		prev2X = tailX[i];
		prev2Y = tailY[i];
		tailX[i] = prevX;
		tailY[i] = prevY;
		prevX = prev2X;
		prevY = prev2Y;
	}
	
	switch (dir)
	{
	case Left:
		x--;
		head = '<';
		break;
	case Right:
		x++;
		head = '>';
		break;
	case Up:
		y--;
		head = '^';
		break;
	case Down:
		y++;
		head = 'v';
		break;
	default:
		break;
	}
	if (x > width || x < 0 || y > height || y < 0)
	{
		GameOver = true;
	}
	if (x == fruitX && y == fruitY){
		fruitX = rand() % width;
		fruitY = rand() % height;
		score += 10;
		ntail++;
	}
	for (int k = 0; k < ntail; k++)
	{
		if (tailX[k] == x && tailY[k] == y)
		{
			GameOver = true;
		}
	}
}

int main(){
	char YESorNo;
	
	do
	{
		SetUp();
		while (!GameOver)
		{
			Sleep(200);
			Draw();
			Input();
			if (!pause){
				Logic();
			}
		}

		system("cls");
		cout << "GAME OVER" << endl;
		cout << "Score: " << score << endl;
		cout << "Do you want to replay? (Respond with y or n)" << endl;
		cin.get(YESorNo);
		cin.get();
		if (YESorNo == 'y' || YESorNo == 'Y')
		{
			GameOver = false;
		}
		if (YESorNo == 'n' || YESorNo == 'N')
		{
			GameOver = true;
		}
	} while (!GameOver);
	
	return 0;
}

[naaissus]

1. when the snake eats at least one fruit, the 'y' for replay option doesn't work

You need to reset ntail to 0 in SetUp().

switch (cin.get()) {
  case 'w':
    dir = Up;
    break;
...

Why don't you use _getch() instead of cin.get().
That way you don't need to press enter every time.

[XYTetris]

Thanks for that answer! Also it was _getch() before. I was just trying to understand the difference between the two commands so I swapped it in. Guess I forgot to switch it back.