Card Shuffle Help

i need to shuffle an array of cards and simply print them in a simple order but i dont know where to go from here, please help.

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>


int main()
{
        char suit[4][0]={"Hearts", "Diamonds", "Spades", "Clubs"};
        char deck[51] {"H2", "H3", "H4", "H5", "H6", "H7", "H8", "H9", "H10", "HJ", "HQ", "HK", "HA",
              "D2", "D3", "D4", "D5", "D6", "D7", "D8", "D9", "D10", "DJ", "DQ", "DK", "DA",
              "S2", "S3", "S4", "S5", "S6", "S7", "S8", "S9", "S10", "SJ", "SQ", "SK", "SA",
              "C2", "C3", "C4", "C5", "C6", "C7", "C8", "C9", "C10", "CJ", "CQ" "CK", "CA"};
        int card;
       
       
_getch();
return 0;
}

---

FYI.

Most C compilers ignore white space, which means as a courtesy to us all, you can split long lines and make it multiple short lines.

And the last time I counted, there were 52 cards in a deck. ;)

Todd

To shuffle the deck you can swap positions in the array something like:

Code:

---

#include <stdlib.h>
#include<ctime.h>

int main()
{
    srand(time(NULL)); //Seed randomisation

    int deck[52];
    int i, temp, random;
    // Init deck
    for(i=0; i<52; i++)
        deck[i] = i;
    //Shuffle deck
    for(i=0; i<52; i++)
    {
        random = rand() % 52;
        temp = deck[ i ];
        deck[ i ] = deck[ random ];
        deck[ random ] = temp;
    }
}

---

Also you can use an integer value to hold the card. card value % 13 will get the rank and card value / 13 the suit. You could then get the relevant text using functions something like:

Code:

---

const char* GetSuit(Uint8 card)

{

    static const char *suit[] = {"Clubs", "Diamonds", "Hearts", "Spades"};

    return suit[card/13];   

}



const char* GetRank(Uint8 card)

{

    static const char *rank[] = {"Ace", "Two", "Three", "Four", "Five",

        "Six", "Seven", "Eight", "Nine", "Ten", "Jack", "Queen", "King"};

    return rank[card%13]; 

}

---

i have this but it doesnt seem to work i have to terminate the program and it comes up with lots of errors.

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <stdlib.h>
#include <time.h>


int main()
{
    srand(time(NULL)); //Seed randomisation

    int deck[52];
    int i, temp, random;
    // Init deck
    for(i=0; i<52; i++)
        deck[i] = i;
    //Shuffle deck
    for(i=0; i<52; i++)
    {
        random = rand() % 52;
        temp = deck[ i ];
        deck[ i ] = deck[ random ];
        deck[ random ] = temp;
                printf("%s", deck[i]);
               
    }
return 0;
}

---

You can't print an integer using %s.

well heres the problem now, i can get it to display random numbers 1 through 52 but they should not repeat and also must be like a deck of cards with Jacks queens kings and aces

Your shuffle doesn't repeat numbers. You need to print outside the shuffle loop.

And everyone else is going to tell you what mike_g told you (about getting names), so I'm not even going to type it -- just look up and pretend I said it again, but louder this time.

from here how could i make it so each card takes a suit?

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <stdlib.h>
#include <time.h>
#include <conio.h>


int main()
{
    srand(time(NULL)); //Seed randomisation

        char suit[4][0]= {"Hearts", "Spades", "Clubs", "Diamonds"}
        char rank[] = {"Ace", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Jack", "Queen", "King"};
            int deck[52];
               
    int i, temp, random;
    // Init deck
    for(i=0; i<52; i++)
        deck[i] = i;
    //Shuffle deck
    for(i=0; i<52; i++)
    {
        random = rand() % 52;
        temp = deck[i];
        deck[i] = deck[ random ];
        deck[ random ] = temp;               
               
    }
        printf("%d", deck[i]);
_getche();
return 0;
}

---

Quote:

---

Originally Posted by killmequick

from here how could i make it so each card takes a suit?

---

And everyone else is going to tell you what mike_g told you (about getting names), so I'm not even going to type it -- just look up and pretend I said it again, but even louder this time.

Quote:

---

Originally Posted by killmequick

Code:

---

char suit[4][0]= {"Hearts", "Spades", "Clubs", "Diamonds"}
char rank[] = {"Ace", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Jack", "Queen", "King"};

---

---

I don't expect either of those array declarations to work. The first declares an array of zero length which is not legal. The second declares an array of characters of unknown length instead of a 2D array of chars, or an array of pointers to chars.

so how would i write an array that works

i am not supposed to use constant characters with this program

Why not? contsant char would be more suitable since you wont want to be editing the content. Never the less, all you would have to do is copy the code from the functions I posted and remove the 'const' part. IE:

Code:

---

int main()
{
    char *suit[] = {"Clubs", "Diamonds", "Hearts", "Spades"};
}

---

The simplest way is to generate a randon number between 1 and 51, then split the array into
two at that point and then make a new array, with the botton half of the split above the top
half, then copy the result back to the original array. Repeat as necessary. That is how a real shuffle is done.
I guess you could mix this with 'fancy shuffles' where you split the pack in to to halfs and then merge them
into the order (for halfs 'a'' and 'b') a[0], b[0], a[1]], b[1], a[2], b[2], etc....



Or perhaps quicker and simpler, select a card at a random position and put it into a new array
in first position, then select another and put it the next position. If the card has already been selected use the first unselected card after it in the array. That is probably the fastest way. But is gets less effiecient towards the end.

I disagree - the algorithm mike suggested is the Knuth shuffle, which is a good shuffle because every card has an equal probability to be swapped with every other card. It's difficult to implement correctly, but I doubt it's any less efficient than what you've suggested. And in all honesty, I'd rather use a documented algorithm for shuffling. I don't think my feelings are that exceptional.

Quote:

---

Originally Posted by citizen

I disagree - the algorithm mike suggested is the Knuth shuffle, which is a good shuffle because every card has an equal probability to be swapped with every other card. It's difficult to implement correctly, but I doubt it's any less efficient than what you've suggested. And in all honesty, I'd rather use a documented algorithm for shuffling. I don't think my feelings are that exceptional.

---

Yes mikes algotithm is better (I did say probably the most efficient :)), actually my method is The original Fisher-Yates (Kunth) method as described in wikipedia. My first thought was to swop two random positions, but I didn't like that much because you call rand twice per iteration, so I came up with the original Fisher-Yates shuffle, but that works fine in theory but is inefficient when you do it on a computer. Incidently I think mike has 53 cards in his pack!! (0-52)! (Well at least room for 53 anyway).

Also I don't think you need to step to the last card in the pack as the chance it will be in that position, at that stage is 1 in 52 (I think) which is the same as any other position, but I guess it will do no harm to, however I think the Kunth method does not step to the last card anyway for the reason I described.

I really see nothing strange with mike's deck of cards, though. the indices are 0 to 51. On the last iteration of his shuffling loop, i is 52, which would break it properly.

And you can't exclude cards in the modern algorithm, otherwise your shuffle has a bias towards the card placement. Your generator could still select any of 52 indices to swap the last one with.

Quote:

---

Originally Posted by citizen

I really see nothing strange with mike's deck of cards, though. the indices are 0 to 51. On the last iteration of his shuffling loop, i is 52, which would break it properly.

And you can't exclude cards in the modern algorithm, otherwise your shuffle has a bias towards the card placement. Your generator could still select any of 52 indices to swap the last one with.

---

Yes I was wrong about the 53 cards thing, I always get confused with indexes and counts, but you can exclude stepping to the last card for swapping because the chance that it has been moved elsewhere through swopping is 50/51 which is already the same as any of the other cards. So it has not been excluded from the randomising algorithm, it just was not necessary to step to it because it's position would be already random due to the chance of it being moved by one of the previous swops. But it does no real harm to step to it barring a very slight increase in run time.
Actually mikes allgorithm does step to the last card (I think) which is strictly unnecessary, and is possible why I got confused about the number of cards
he was using.

Incidently I don't really understand why C starts it's array indexes with 0 rather than 1, however I think I have mentioned that before, it would certaintly have saved me a lot of grief in the past (and present and future no doubt!!).

mike, i get a lot of errors with this..

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <stdlib.h>
#include <time.h>
#include <conio.h>


int main()
{
       
    srand(time(NULL)); //Seed randomisation
        /*char* GetSuit(Uint8 card){

        char *suit[] = {"Clubs", "Diamonds", "Hearts", "Spades"};
        return suit[card/13];
        }
        char* GetRank(Uint8 card)
        {
        char *rank[] = {"Ace", "Two", "Three", "Four", "Five",

        "Six", "Seven", "Eight", "Nine", "Ten", "Jack", "Queen", "King"};
        return rank[card%13];
        }*/
            int deck[52];
               
    int i, temp, random;
    // Init deck
    for(i=0; i<52; i++)
        deck[i] = i;
    //Shuffle deck
    for(i=0; i<52; i++)
    {
        random = rand() % 52;
        temp = deck[i];
        deck[i] = deck[ random ];
        deck[ random ] = temp;               
               
    }
                char* GetSuit(Uint8 card){

        char *suit[] = {"Clubs", "Diamonds", "Hearts", "Spades"};
        return suit[card/13];
        }
        char* GetRank(Uint8 card)
        {
        char *rank[] = {"Ace", "Two", "Three", "Four", "Five",

        "Six", "Seven", "Eight", "Nine", "Ten", "Jack", "Queen", "King"};
        return rank[card%13];
        }
        printf("%d", deck[i]);
_getche();
return 0;
}

---

The main problem is that you have some functions written multiple times as well as inside of main(). Don't do that - write them once, somewhere else in the file.

the first section was commented out..but unfortunetley anyway i write this code i get errors. One beings that card is not defined..what is card supposed to be defined as? Here is code without the extra junk.

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <stdlib.h>
#include <time.h>
#include <conio.h>


int main()
{
       
        char *suit[] = {"Clubs", "Diamonds", "Hearts", "Spades"};
        return suit[card/13];
        char *rank[] = {"Ace", "Two", "Three", "Four", "Five",

        "Six", "Seven", "Eight", "Nine", "Ten", "Jack", "Queen", "King"};
        return rank[card%13];
       
    srand(time(NULL)); //Seed randomisation

            int deck[52];
               
    int i, temp, random;
    // Init deck
    for(i=0; i<52; i++)
        deck[i] = i;
    //Shuffle deck
    for(i=0; i<52; i++)
    {
        random = rand() % 52;
        temp = deck[i];
        deck[i] = deck[ random ];
        deck[ random ] = temp;               
               
    }
       
       
        printf("%d", deck[i]);
_getche();
return 0;
}

---

Oh, yeah you want to remove the line that start with 'return' from main, but leave the return 0 at the end. Returning from main will basically quit your program.

I find it simpler just to provide my own example than try to fix your version. The problem is that card is supposed to be a number in the pack. In your code, there used to be functions for finding out the pips on a card, and the suit of the card. Like this:

Code:

---

#include <stdlib.h>
#include <time.h>
#include <stdio.h>

const char * what_pip( int this_card );
const char * what_suit( int this_card );
void make_deck( int * this_deck );
void shuffle( int * this_deck );

int main ( void )
{
    int mypack[52];
    long card;

    make_deck( mypack );
    srand( (unsigned )time( NULL ) );
    shuffle( mypack );
   
    for ( card = 0; card < 52; card += 4 ) {
        printf( "&#37;s%s %s%s %s%s %s%s\n",
            what_pip( mypack[card] ), what_suit( mypack[card] ),
            what_pip( mypack[card + 1] ), what_suit( mypack[card + 1] ),
            what_pip( mypack[card + 2] ), what_suit( mypack[card + 2] ),
            what_pip( mypack[card + 3] ), what_suit( mypack[card + 3] ) );
    }
    return 0;
}

const char * what_pip( int this_card )
{
    const char * pips[] = {
        "A", "2", "3", "4", "5", "6", "7", "8", "9",
        "T", "J", "Q", "K"
    };
    return pips[ this_card % 13 ];
}

const char * what_suit( int this_card )
{
    const char * stacks[] = { "S", "H", "C", "D" };
    return stacks[ this_card / 13 ];
}

void make_deck( int * this_deck )
{
    long idx;
    if ( this_deck == NULL ) return ;

    for ( idx = 0; idx < 52; idx++ ) {
        this_deck[idx] = idx;
    }
}

void shuffle ( int * this_deck )
{
    long idx;
    if ( this_deck == NULL ) return ;

    for ( idx = 0; idx < 52; idx++ ) {
        int rnd = rand() / RAND_MAX / 52;
        int save = this_deck[idx];
        this_deck[idx] = this_deck[rnd];
        this_deck[rnd] = save;
    }
}

/** my output -
TS 7D 5H JS
AD JD 7S 3D
QC 7C JH JC
KS 6H TD KD
2S 8H 9H 3C
QS QH TC 5C
TH QD 8S AH
AS 4H 4S 5D
4C 6S KH KC
6D 9C 5S 8D
7H 3S 6C 2H
8C 2C 9D 9S
3H 4D AC 2D
**/

---

Nice and shuffled.

the only problem with what you have done is that the cards dont print out randomely

Dude, just remove the return statements from your code :o

And the only problem with what your post says is I'm not sure what the problem is.

If you're running the executable multiple times in quick succession expecting a very different result each time, then rand() has a seed which isn't very good. If you're shuffling the same deck multiple times and the results aren't very different, you need a different approach to calling rand(), because the card selection is suffering from bias. You might want to read using rand() effectively to get some ideas on what to do about this (and how a PRNG will affect your card games in general).

If you are trying to write a casino program and this isn't some academic venture, then you will have to write a stronger PRNG anyway, since rand() is not cryptographically random and wouldn't do for like, online poker. If you're looking for something with that kind of effectiveness, you need to learn and weigh these approaches.

If my code is wrong because I chose to print out the whole deck in four columns so you could see the result of the shuffle, I'm sorry. You'll have to work out how to deal cards for the game you are playing yourself.