C#•2y ago

❔ Null instance in Array of Classes

Hey guys. It's my first time here, so sorry for any formatting errors or something like that. I'm making this program where I need to create an array of objects of a class. The compiler doesn't detect any errors, but when I try to modify an instance in the array he tells me that that instance is null.

CreateCards();

void CreateCards()
{
    int colorNumber = 1;
    int rankNumber = 1;
    int currentCard = 1;
    string color;
    string rank;

    Card[] cards = new Card[1];

    //this is where the program crashes and the compiller tells me cards[] is null
    cards[0].CardColor = CardColor.zero; 
}

class Card
{
    public CardColor CardColor { get; set; } = CardColor.zero;
    public CardRank CardRank { get; set; } = CardRank.zero;
    public bool isFace { get; }

    public Card ()
    {
        CardColor = CardColor.zero;
        CardRank = CardRank.zero;
        if (CardRank == CardRank.cifrao || CardRank == CardRank.porcentagem ||
            CardRank == CardRank.circunflexo || CardRank == CardRank.ampersand) isFace = true;
    }
}

enum CardColor { zero, red, green, blue, yellow}
enum CardRank { zero, one, two, three, four, five, six, seven, eight, nine, ten, cifrao, porcentagem, circunflexo, ampersand}

CreateCards();

void CreateCards()
{
    int colorNumber = 1;
    int rankNumber = 1;
    int currentCard = 1;
    string color;
    string rank;

    Card[] cards = new Card[1];

    //this is where the program crashes and the compiller tells me cards[] is null
    cards[0].CardColor = CardColor.zero; 
}

class Card
{
    public CardColor CardColor { get; set; } = CardColor.zero;
    public CardRank CardRank { get; set; } = CardRank.zero;
    public bool isFace { get; }

    public Card ()
    {
        CardColor = CardColor.zero;
        CardRank = CardRank.zero;
        if (CardRank == CardRank.cifrao || CardRank == CardRank.porcentagem ||
            CardRank == CardRank.circunflexo || CardRank == CardRank.ampersand) isFace = true;
    }
}

enum CardColor { zero, red, green, blue, yellow}
enum CardRank { zero, one, two, three, four, five, six, seven, eight, nine, ten, cifrao, porcentagem, circunflexo, ampersand}

6 Replies

Anton•2y ago

yes that's how it works. read on reference types the default value for a reference type is null

baykkzOP•2y ago

and how would I define the value for all instances of the array here?

mrphil2105•2y ago

When you new up an array you get an array of the default value The default value of a class (aka reference type) is null So you need to go through the array and initialize

for (int i = 0; i < arr.Length; i++)
{
    arr[i] = new Foo();
}

for (int i = 0; i < arr.Length; i++)
{
    arr[i] = new Foo();
}

Foo being Card here What you are doing now is accessing something on null, not valid

baykkzOP•2y ago

oh, think I got it let me try this this worked perfectly!! Also got how it works Thank you so much @mrphil2105 !!

mrphil2105•2y ago

👍

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Null instance in Array of Classes