Trouble with C# array

Question

Hi, I am writing a card playing program as a way of learning C#.

I ran into an issue with an array going out of bounds.

Here is my code:

namespace Pcardconsole
{
    class Deck
    {
        public Deck()
        {
            // Assign standard deck to new deck object
            int j;
            for (int i = 0; i != CurrentDeck.Length; i++)
            {
                CurrentDeck[i] = originalCards[i];
            }
            // Fisher-Yates Shuffling Algorithim
            Random rnd = new Random();

            for (int k = CurrentDeck.Length - 1; k >= 0; k++)
            {
                int r = rnd.Next(0, k + 1);

                int tmp = CurrentDeck[k];
                CurrentDeck[k] = CurrentDeck[r];
                CurrentDeck[r] = tmp;
            //    Console.WriteLine(i);
            }
        }

        public void Shuffle()
        {
            // TODO
        }
     //   public int[] ReturnCards()
      //  {
         // TODO
      //  }

        public int[] originalCards = new int[54]
        {
            0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C,

            0x1D, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2A, 0x2B, 

            0x2C, 0x2D, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 

            0x3B, 0x3C, 0x3D, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 

            0x4A, 0x4B, 0x4C, 0x4D, 0x50, 0x51
        };

        public int[] CurrentDeck = new int[54];

    }

    class Program
    {
        static void Main(string[] args)
        {
            // Create a Deck object
            Deck mainDeck = new Deck();
            Console.WriteLine("Here is the card array:");
            for (int index = 0; index != mainDeck.CurrentDeck.Length; index++)
            {
                string card = mainDeck.CurrentDeck[index].ToString("x");
                Console.WriteLine("0x" + card);
            }
        }
    }
}

The hexidecimal numbers stand for different cards.

When I compile it I get an array index out of bounds error, and a crash.

I don't understand what is wrong.

Any help would be much appreciated.

Answer 1

Shouldn't this be

for (int k = CurrentDeck.Length - 1; k >= 0; k--)

instead of

for (int k = CurrentDeck.Length - 1; k >= 0; k++)

Also you can store the length property to a variable and then check against that variable.

int currentDeckLength = CurrentDeck.Length;

for (int k = currentDeckLength - 1; k >= 0; k++)

Answer 2

You should make your loop decrease: k-- instead of k++.

By incrementing it you are accessing an out of bound index since you initialized k at the max count to begin with. Your loop looks like it is setup to loop backwards, so decrement the index.

Answer 3

You have for (int k = CurrentDeck.Length - 1; k >= 0; k++)

It should be for (int k = CurrentDeck.Length - 1; k >= 0; k--)

Do you see the difference?