Snake game in C++ for Windows console

Question

To give you a simple background, I've been programming in C++ for about a week and decided I wanted to build a simple snake game.

I made one over the course of a day and this is the end result. What overall improvements can be made to this code? Are there any general advice on programming that might be relevant?

#include <iostream>
#include <map>
#include <cstdlib>
#include <conio.h>
#include <cmath>
#include <vector>
#include <ctime>

using namespace std;

const int boardX = 40, boardY = 20;
int center = ceil ((boardX/2*boardY)-(boardX/2));

map<int, char> gameMap;
map<int, char>::const_iterator it;

int snakeXY = center;
enum snakeDir {UP,DOWN,LEFT,RIGHT};
snakeDir direction;
vector<int> tailPieces;

bool fruitSpawned=false;
bool stopped;
bool gameOver;

// Creates and places all the elements into the map (gameMap)
void createMap(){
    for(int i = 1; boardX*boardY>=i; i++){ 
        if((i<=boardX) || (i>(boardX*boardY-boardX))){ 
            gameMap[i] = '#';
        } else if((i % boardX == 0) || ((i-1) % boardX == 0)){ 
            gameMap[i] = '#';
        } else {
            gameMap[i] = ' ';
        }
    }
}

// Handles input from the user
void keyUpdate(){
    char key;

    if(kbhit() == true){
        key = getch();

        switch(key){
            case 'w':
            case 'W':
                direction = UP;
                break;
            case 'a':
            case 'A':
                direction = LEFT;
                break;
            case 's':
            case 'S':
                direction = DOWN;
                break;
            case 'd':
            case 'D':
                direction = RIGHT;
                break;
            case 'P'
            case 'p'
                if(!stopped){
                    stopped = true;
                } else {
                    stopped = false;
                }
            default:
                break;
        }
    }
}

// Handles hit detection, snake's head and tail movement
void updateSnake(){
    int prevXY = snakeXY;

    if(!stopped){
        switch(direction){
            case UP:
                snakeXY = snakeXY - boardX;
                break;
            case DOWN:
                snakeXY = snakeXY + boardX;
                break;
            case LEFT:
                --snakeXY;
                break;
            case RIGHT:
                ++snakeXY;
                break;
        }

       if(!stopped){
            if(tailPieces.empty()){
                gameMap[prevXY] = ' ';
            } else {

                int tailPieceXY;

                for(int i = 0; i <= tailPieces.size(); i++){
                    if (i == tailPieces.size()){
                        gameMap[prevXY] = ' ';
                    } else {
                        tailPieceXY = tailPieces[i];
                        tailPieces[i] = prevXY;
                        gameMap[prevXY] = 'o';
                        prevXY = tailPieceXY;
                    }
                }
            }
            if(gameMap[snakeXY] == '#' || gameMap[snakeXY] == 'o'){
                gameOver = true;
            } else if(gameMap[snakeXY] == 'F') {
                tailPieces.push_back(prevXY);
                gameMap[snakeXY] = 'O';
                fruitSpawned = false;
            } else {
                gameMap[snakeXY] = 'O';
            }
        }
    }
}

// Draws the map into the cmd console.
void updateMap(){
    system("cls");
    for (it = gameMap.begin(); it!= gameMap.end(); it++){
            cout << it->second;
        if(it->first % boardX == 0){
            cout << endl;
        }
    }
}

// Determines locations for the fruit, and spawns them accordingly.
void spawnFruit(){

    vector<int> safeSpace;

    for (it = gameMap.begin(); it!= gameMap.end(); it++){
        if(it->second == ' '){
            safeSpace.push_back(it->first);
        }
    }

    srand(time(NULL)); // Seeding for randomness
    int random = rand() % safeSpace.size();
    gameMap[safeSpace[random]] = 'F';
    fruitSpawned = true;

}


int main(){
    createMap();

    gameOver = false;
    stopped = false;

    while(!gameOver){
        updateMap();
        updateSnake();
        if(!fruitSpawned){
            spawnFruit();
        }
        keyUpdate();
        _sleep(125);
    }


    return 0;
}

Answer 1

Bugs

Line 61 and onward:

case 'd':
case 'D':
    direction = RIGHT;
    break;
    case 'P'
        case 'p'
        if (!stopped) {
            stopped = true;
        }
        else {
            stopped = false;
        }
        default:
            break;
}

case 'P' and case 'p' are missing a : at the end. Without them your code will not compile.

Also keep in mind your indentation is off. The correct implementation would be:

case 'd':
case 'D':
    direction = RIGHT;
    break;
case 'P':
case 'p':
    if (!stopped) {
        stopped = true;
    }
    else {
        stopped = false;
    }
default:
    break;
}

Deprecations

In that same function, you're using kbhit() and getch(). Those are deprecated IIRC. Use the underscored versions instead, like this:

if (_kbhit() == true) {
    key = _getch();

Your sleep function is also deprecated. Since you're developing for Windows-only, consider using #include <windows.h> and use Sleep(125); in your main.

Another deprecation is the return 0; at the end of your main. It will be added by the compiler under the hood, no need to state it explicitly. This is since C++98.

Namespaces

using namespace std; is considered bad practice. Short code is not a requirement in C++, clear code is preferred. It's a thing commonly taught to new C++ programmers because it's 'easier', but it will royally bite you in the behind when conflicts arise.

Input

keyUpdate();

That's how you get your input. But that's not how you want to get your input. You want to handle your input real-time. You want an EventHandler to handle a KEY_EVENT. Now you can handle your input non-blocking and decouple the FPS from the main loop :-)