Simple casino game

Here are a few suggestions:

• Give more instructions for user input and validate it carefully. I tried out the program, entered "1.", and immediately got stuck in an infinite loop.
• It is much clearer when functions are declared before use. When two functions depend on each other, there is a better solution >99% of the time.
• Mutable (i.e. not constant) global variables add complexity because they are essentially hidden parameters for every function. There is a better solution >99% of the time.
• Be careful comparing money (double) to 0 (int). In general, integers are preferable for currencies because they have consistent precision. You can make the smallest unit something like 0.000001 dollars.
• Use functions for repeated code, such as getting input or asking for a bet.
• Make your error messages as precise as possible. As an example, you might want a separate message for negative bets.

Here's the implementation with suggestions for the first game:

#include <iostream>
#include <string>
#include <sstream>
#include <ctime>

using namespace std;

// type input and press enter
stringstream getline_stream() {
    string user_input;
    getline(cin, user_input);
    return stringstream(user_input);
}

// asks the user to enter a bet
int get_bet(int money) {
    while (true) {
        cout << "\nYou have " << money << " dollars.\n";
        cout << "Please enter your bet (integer >= 0).\n";

        int bet;
        getline_stream() >> bet;

        if (bet > money) {
            cout << "You do not have enough money!\n";
            continue;
        }

        if (bet < 0) {
            cout << "You cannot bet a negative amount!\n";
            continue;
        }

        return bet;
    }
}

// returns your money after playing Guess The Number
int guess_the_number(int money) {
    cout << "\nYou are playing Guess The Number!\n";
    cout << "If you win, you receive double your bet!\n";
    int answer = (rand() % 10) + 1;

    // get a valid bet
    int bet = get_bet(money);
    money -= bet;

    // get the guess
    cout << "\nPlease type your guess and press enter.\n";
    cout << "The answer is an integer from 1 to 10 inclusive.\n";
    int guess;
    getline_stream() >> guess;

    cout << "\nThe correct answer was " << answer << ".\n";
    if (guess == answer) {
        cout << "Congratulations, you win!\n";
        return money + 2 * bet;
    }
    else {
        cout << "Sorry, you lose!\n";
        return money;
    }
}

int main()
{
    // initialize the random number generator
    srand(static_cast<unsigned int>(time(0)));

    // welcome message
    cout << "Hello! Welcome to my casino.\n";
    int money = 100;

    // dialogue loop
    while (true) {
        cout << "\nYou have " << money << " dollars.\n";
        cout << ">> Quit: type 'q' and press enter.\n";
        cout << ">> Reset: type 'r' and press enter.\n";
        cout << ">> Guess The Number: type '1' and press enter.\n";
        cout << ">> Blackjack: type '2' and press enter.\n";

        char choice;
        getline_stream() >> choice;

        switch (choice) {
        case 'q':
            return 0;
        case 'r':
            money = 100;
            break;
        case '1':
            money = guess_the_number(money);
            break;
        case '2':
            money = blackjack(money);
            break;
        default:
            cout << "\nYour input could not be parsed.\n";
        }
    }
}

Good job on a well-contained MVP. Hope this helps!

Blackjack (Update)

// text for each card
const char cards[13][3] = {
    "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A" };

// gets a card index
int get_index() {
    return rand() % 13;
}

// updates number of aces, number of other points
void update_state(int *other, int *aces, int index) {
    if (index < 9) // 2 to 10
        (*other) += index + 2;
    else if (index < 12) // J, Q, K
        (*other) += 10;
    else // A
        (*aces) += 1;
}

// gets best score, avoid bust if able
int best_with_bust(int other, int aces) {
    int score = other + 11 * aces;

    for (int i = 0; i < aces; ++i)
    {
        if (score <= 21)
            return score;
        score -= 10;
    }

    return score;
}

// returns your money after playing Blackjack
int blackjack(int money) {
    cout << "\nYou are playing Blackjack!\n";
    cout << "If you win, you receive double your bet!\n";

    // get a valid bet
    int bet = get_bet(money);
    money -= bet;

    // game state
    int p_other = 0;
    int p_aces = 0;
    int d_other = 0;
    int d_aces = 0;

    // player's first draw
    int p_index = get_index(); 
    cout << "\nYou draw " << cards[p_index] << ".\n";
    update_state(&p_other, &p_aces, p_index);

    // dealer's first draw
    int d_index = get_index();
    cout << "The dealer draws " << cards[d_index] << ".\n";
    update_state(&d_other, &d_aces, d_index);

    // player's draws
    int p_score;
    while (true)
    {
        p_index = get_index();
        cout << "\nYou draw " << cards[p_index] << ".\n";
        update_state(&p_other, &p_aces, p_index);
        p_score = best_with_bust(p_other, p_aces);

        // bust
        if (p_score > 21) {
            cout << "Sorry, you lose by bust!\n";
            return money;
        }

        // natural 21
        if (p_score == 21)
            break;

        // hit or stand
        cout << ">> Hit: type 'h' and press enter.\n";
        cout << ">> Stand: type 's' and press enter.\n";

        char hit_or_stand;
        getline_stream() >> hit_or_stand;
        if (hit_or_stand == 's')
            break;
    }

    cout << "\nYou stand with " << p_score << " points.\n";

    // dealer's draws
    int d_score;
    while (true) {
        d_index = get_index();
        cout << "The dealer draws " << cards[d_index] << ".\n";
        update_state(&d_other, &d_aces, d_index);
        d_score = best_with_bust(d_other, d_aces);

        // bust
        if (d_score > 21) {
            cout << "\nCongratulations, you win by dealer bust!\n";
            return money + 2 * bet;
        }

        // hit or stand
        if (d_score > 16)
            break;
    }

    cout << "\nThe dealer stands with " << d_score << " points.\n";

    // win by comparison
    if (p_score > d_score) {
        cout << "Congratulations, you win!\n";
        return money + 2 * bet;
    }

    // tie by comparison
    if (p_score == d_score) {
        cout << "It's a tie!\n";
        return money + bet;
    }

    // lose by comparison
    cout << "Sorry, you lose!\n";
    return money;
}

Imitating Blackjack logic is rather complicated, but here was my best attempt. Simplifying the checks can be done by reducing chances for user input (e.g. automate the treatment of aces as 1 or 11) and different methods of control flow, like continue, break, and return. Note that I pass references (pointers) instead of values to update_state. Pointers are a rather infamous topic, but I think a small example like this one could be illustrative. Feel free to ask questions.

Some things not mentioned in other answers:

• What's the problem with "using namespace std;"?
• std::endl does more than just newline, so don't use it unless you really need to flush output (arguably even then, prefer to write std::flush separately).

In general, I would avoid using global variables. Variables such as pHand should be defined in blackJack and then passed by reference to checkStand and addPlayerCard.

For the global variables that you determine do need to remain global, you can look into creating a header file that can be included. You could call such a header file defaults.h. You could also move your function headers into a header file as well.

I would suggest getting rid of main2 and putting the code from main2 back into main. Then, I would take a crack at avoiding recursively calling main or any of the other functions, as it is not needed, and could cause a crash if you were to continue playing long enough.

Here is the fix I suggest for this, without altering the code too much:

Your main function could look something like this:

int main()
{
    int choice = 0;
    srand(static_cast<unsigned int>(time(0)));

    while (true) {
        if (money == 0) {
            cout << "Sorry you hit 0 dollars" << endl;
            return 0;
        }
        cout << "Hello! Welcome to my casino. \n" << "Which game would you like to play? \n" << "1. Guess the number \n" << "2. Blackjack \n" << "3. Quit \n";
        cin >> choice;
        system("cls");
        switch (choice) {
            case 1:
                numberguess();
                break;
            case 2:
                blackJack();
                break;
            case 3:
                return 0;
            default:
                cout << "This is not a valid answer \n";
        }
    }

    return 0;
}

Notice that I moved the declaration and instantiation of choice to the top of main, and out of the body of the while loop. While modern compilers will optimize that out for you, it is good practice to avoid re-declaration of variables.

If you apply the fix I suggested for main, you could then remove the code asking if the player would like to play again in blackJack and numberguess, as the main function can now properly handle that. You could then remove the calls to main as well.