How does this source code know that gameOver means to turn off?

[gameguy8888]

I've been studying a snake game program but I can't figure out how the program knows how gameOver means to turn off.

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

bool gameOver;

const int width = 20;
const int height = 10;

int x, y, fruitX, fruitY, score;
int tailX[100], tailY[100];
int nTail;

enum eDirecton { STOP = 0, LEFT, RIGHT, UP, DOWN};
eDirecton dir;

void Setup()
{
gameOver = false;
dir = STOP;
x = width / 2;
y = height / 2;
fruitX = rand() % width;
fruitY = rand() % height;
score = 0;
}
void Draw()
{
system("cls"); //system("clear");
for (int i = 0; i < width+2; i++)
cout << "1";
cout << endl;

for (int i = 0; i < height; i++)
{
for (int j = 0; j < width; j++)
{
if (j == 0)
cout << "2";
if (i == y && j == x)
cout << "O";
else if (i == fruitY && j == fruitX)
cout << "y";
else
{
bool print = false;
for (int k = 0; k < nTail; k++)
{
if (tailX[k] == j && tailY[k] == i)
{
cout << "o";
print = true;
}
}
if (!print)
cout << " ";
}


if (j == width - 1)
cout << "4";
}
cout << endl;
}

for (int i = 0; i < width+2; i++)
cout << "4";
cout << endl;
cout << "Score:" << score << endl;
}
void Input()
{
if (_kbhit())
{
switch (_getch())
{
case 'a':
dir = LEFT;
break;
case 'd':
dir = RIGHT;
break;
case 'w':
dir = UP;
break;
case 's':
dir = DOWN;
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--;
break;
case RIGHT:
x++;
break;
case UP:
y--;
break;
case DOWN:
y++;
break;
default:
break;
}
//if (x > width || x < 0 || y > height || y < 0)
// gameOver = true;
if (x >= width) x = 0; else if (x < 0) x = width - 1;
if (y >= height) y = 0; else if (y < 0) y = height - 1;

for (int i = 0; i < nTail; i++)
if (tailX[i] == x && tailY[i] == y)
gameOver = true;

if (x == fruitX && y == fruitY)
{
score += 10;
fruitX = rand() % width;
fruitY = rand() % height;
nTail++;
}
}
int main()
{
Setup();
while (!gameOver)
{
Draw();
Input();
Logic();
Sleep(30); //sleep(10);
}
return 0;
}

[megatron 0]

while (!gameOver)

gameOver is a boolean value that can be set to true or false. Because gameOver is a global variable, anything can change it, heance when it changes in the functions, it also changes in the while loop.