My Snake Game Progarm in C++

# include<iostream>
# include<conio.h>
void run();
void printMap();
void initMap();
void move(int dx, int dy);
void update();
void changeDirection(char key);
void clearScreen();
void generateFood();
char getMapValue(int value);

const int mapwidth = 20;
const int mapheight = 20;

const int size = mapwidth + mapheight;

int map[size];
int headxpos;
int headypos;
int direction;

int food = 3;

bool running;

int main()
{
run();
return 0;
}
void run()
{
initMap();
running = true;
while(running)
{
if (_kbhit()) { changeDirection(_getch()); }
update();
clearScreen();
printMap();
}
    std::cout << "\t\t!!!Game over!" << std::endl << "\t\tYour score is:" << food;
std::cin.ignore();
}
void changeDirection(char key)
{
switch (key) {
case'w':
if (direction != 2) direction = 0;
break;
case'd':
if (direction != 3) direction = 1;
break;
case's':
if (direction != 4) direction = 2;
break;
case'a':
if (direction != 5) direction = 3;
break;
}
}
void move(int dx, int dy) {
int newx = headxpos + dx;
int newy = headypos + dy;
if (map[newx + newy * mapwidth] == -2) {
food++;
generateFood();
}
else if (map[newx + newy * mapwidth] != 0) {
running = false;
}
headxpos = newx;
headypos = newy;
map[headxpos + headypos * mapwidth] = food + 1;
}
void clearScreen() {
system("cls");
}
void generateFood() {
int x = 0;
int y = 0;
do {
x = rand() % (mapwidth - 2) + 1;
y = rand() % (mapheight - 2) + 1;
} while (map[x + y * mapwidth] != 0);
         map[x + y * mapwidth] = -2;
}
void update() {
switch (direction) {
case 0:move(-1, 0);
break;
case 1:move(0, 1);
break;
case 2:move(1, 0);
break;
case 3:move(0, -1);
break;
}
for (int i = 0;i < size;i++) {
if (map[i] > 0)map[i]--;
}
}
void initMap()
{
headxpos = mapwidth / 2;
headypos = mapheight / 2;
map[headxpos + headypos * mapwidth] = 1;
for (int x = 0;x < mapwidth;++x)
{
map[x] = -1;
map[x + (mapheight - 1) * mapwidth] = -1;
}
for (int y = 0;y < mapheight;y++)
{
map[0 + y * mapwidth] = -1;
map[(mapheight - 1) + y * mapwidth] = -1;
}

generateFood();
}

void printMap()
{
for (int x = 0;x < mapwidth;++x) {
for (int y = 0;y < mapheight;++y) {
std::cout << getMapValue(map[x + y * mapwidth]);
}
std::cout << std::endl;
}
}

char getMapValue(int value)
{
if (value > 0)return'o';
switch (value) {
case -1: return'X';
case -2: return'0';
}
}