存放二十一点手牌的最佳方法？

Question

First off, I'm still new to C, so please let me know about any suggestions you can make (especially about handling arrays).

I want to store a BlackJack hand in C. I've come to the conclusion that a hand or card has to be a string, because cards can be both characters: A, J, Q, K or numbers: 1, 2.. 10 , where 10 should actually be a string of two characters.

Now, I tried storing cards making up a hand into an array like this:

char* hand;
hand[1] = "A";
hand[2] = "2";

The problem is the 10 , which takes up two indices of the array instead of one. A way I could get around this would just be to create a struct with 5 strings (the maximum number of cards in a BlackJack hand), one for each card. However, what if I, for some reason, wanted to have a hand of thousands of cards? What would be the best way to store a hand then?

Answer 1

You might find this site interesting.

http://www.computerpokercompetition.org/

They host an annual AI poker competition. Their server is written in C, and you can download the code from the above site.

Basically, they store the cards as integers. This is the most efficient way of dealing with the cards. There are only 52 types of cards in the deck. More if there are jokers present. So you can map this into an integer value between 0 and 51. They use the following function to print out what a card is, since an integer card number is not going to tell you much. Notice they build the string based on rank and suite.

int printCard( const uint8_t card, const int maxLen, char *string  )
{
  if( 3 > maxLen ) {
    return -1;
  }

  string[ 0 ] = rankChars[ rankOfCard( card ) ];
  string[ 1 ] = suitChars[ suitOfCard( card ) ];
  string[ 2 ] = 0;

  return 2;
}

Answer 2

Don't store the cards as strings (eg "9" ), but as chars (eg '9' ). For the value 10 you could use a replacement char like 'T' . Example code:

char hand[MAX_HAND_LEN];
int hand_len;

get_hand(hand, hand_len);

for (int i = 0; i < hand_len; i++) { 
    if (hand[i] == 'T') {
        putchar('1');
        putchar('0');
    } else {
        putchar(hand[i]);
    }
    putchar(' ');
}
putchar('\n');

This way you neither waste unnecessary memory (since one card now only requires one byte of storage), nor sacrifice code simplicity or readability.

Answer 3

I wrote an essay on the subject here . Using strings is a really bad idea. Integers are better, and the best order to use is to put suit in the low-order bits, ie, use the order 2c, 2d, 2h, 2s, 3c, 3d, ... Ks, Ac, Ad, Ah, As. That way, you don't even have to separate ranks and suits to do the math. Hands, then, are just arrays of integers. I can run billions of hands in minutes with this representation. The function in my library to calculate the total of a blackjack hand looks like this (the OJ_CARD macro expands to an integer constant, so that compare is fast):

int ojb_total(const oj_cardlist_t *sp) {
    int i, c, t = 0, ace = 0, soft = 0;

    for (i = 0; i < sp->length; ++i) {
        c = sp->cards[i];
        if (c >= OJ_CARD(OJR_ACE, OJS_CLUB)) {
            ace = 1;
            ++t;
        } else if (c >= OJ_CARD(OJR_TEN, OJS_CLUB)) {
            t += 10;
        } else {
            t += OJ_RANK(c) + 2;
        }
    }
    if (ace && t < 12) {
        t += 10;
        soft = 1;
    }
    return soft ? -t : t;
}

That's from a general-purpose card simulation library and it's quite fast, but if I really wanted balls-to-the-wall speed from a blackjack simulation that did nothing else, I wouldn't represent cards at all, but just have a "deck" of multiple copies of {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10, 10, 10}, and deal from that.

Answer 4

I'd say there is no single best way. However, char *hand; does not define an array of strings; you could use char *hand[5] , and the 10 would not take two indices; or you could use char hand[5] , and store the 10 as a single character, eg '0' or 'T'.

Answer 5

Store the cards as integers:

• 1 = Ace
• 2 = 2
• 3 = 3
• ...
• 9 = 9
• 10 = 10
• 11 = Jack
• 12 = Queen
• 13 = King

For display purposes, translate the integers to their names using a translate function:

string GetCardNameFromNumber(int cardNumber)
{
    switch(cardNumber)
    {
        case 1:
            return "A";
        case 11:
            return "J";
        case 12:
            return "Q";
        case 13:
            return "K";
        default:
            return cardNumber.ToString();
    }
}