C++ Array Shuffle

Question

I\'m fairly new to C++ and don\'t quite understand function parameters with pointers and references. I have an array of Cards that I want to shuffle using the Fisher-Yates

Answer 1

It looks that your problem does not come from the code posted, which looks fine at a first glance, but from the code around it.

What about using a standard container of cards ? You must fill it, print it first to see if it's ok, shuffle, and then print it again.

#include <vector>
std::vector<Card> deck; // Empty for now. Must be filled with cards.


void shuffle (std::vector<Card> & deck)
{
    int deckSize = 24;
    while (deckSize > 1) 
    {
       long int k = lrand48();
       k = k %24;
       deckSize--;
       Card temp = deck[deckSize];
       deck[deckSize] = deck[k];
       deck[k] = temp;
    }
}

Answer 2

You declared deck as an array of pointers but you didn't allocate any space for it. If you de-reference it without allocating space you will get a seg-fault.

Answer 3

Basic arrays can't be defined with variable passed as size, as mentioned above.

And be careful there. Last element of

typename array[SIZE];

is array[SIZE-1], not array[SIZE]. It's probably where you getting a segfault.

You really should at lest try to use STL containers. STL has shuffle algorithms too (:

Answer 4

Just use std::random_shuffle found in <algorithm>, like this:

std::random_shuffle(deck, deck + deckSize);

and your deck with be shuffled.

Answer 5

I think it might help to see the calling code.

class Card{
public:
    Card(int number):number_(number){}
    int getNumber(){return number_;}
 // ...
private:
    int number_;
};

void shuffle (Card * deck[]) {
    int deckSize = 24;
    while (deckSize > 1) {
       long int k = lrand48();
       k = k %24;
       deckSize--;
       Card * temp = deck[deckSize];
       deck[deckSize] = deck[k];
       deck[k] = temp;
    }
}

int main(int argc, char* argv[]){
{

  const int deckSize=24;
  Card* deck[deckSize];
  for(int i = 0 ; i getNumber()

That should work just fine.

Answer 6

You could also use

std::random_shuffle(deck, deck + deckSize)

which does Fisher-Yates for you.

However, there probably aren't enough bits in the standard random libraries to genuinely choose from all possible random permutations of cards.