Setting jagged array values within a class

Question

I'm having trouble understanding this problem with creating a jagged array in C#. If you look at the code below, it compiles fine. But if I were to take the 2 lines that are assigning values to the array "places" and move them from within the method to within the class itself, the compiler starts complaining with a lot of strange errors.

At first I thought that its because of the usage of the 'new' keyword within a class (a class being just a definition whereas 'new' refers to an instance... you can't have an instance within a definition, can you?). But then I noticed the usage of the 'new' keyword in the initialization of "places" was OK even though it was initialized within the class. Please explain.

public class Place
{
string[][] places = new string[2][];
   public void enumerate()
   {
     places[0] = new string[] { "Canada", "United States" };
     places[1] = new string[] { "Calgary", "Edmonton", "Toronto" };

     Console.WriteLine(places[0][1]);
   }
}

EDIT: to be explicit, the error is produced when running

public class Place
{
string[][] places = new string[2][];
places[0] = new string[] { "Canada", "United States" };
places[1] = new string[] { "Calgary", "Edmonton", "Toronto" };
   public void enumerate()
   {
     Console.WriteLine(places[0][1]);
   }
}

errors received "array size cannot be specified in a variable declaration (try initializing with a "new" expression)" "invalid tokens =, {, in class" "namespace cannot directly contain members such as fields or methods"

Why would you use a jagged array for this? It would be better served as class objects. — OneFineDay
– OneFineDay, Commented Aug 22, 2013 at 19:33
I'm not sure what you mean. Ignore the meaning of the values used. It is a completely meaningless array. I'm just wondering why it won't compile. — Snik
– Snik, Commented Aug 22, 2013 at 19:37
How does that not compile? It did for me output = United States. — OneFineDay
– OneFineDay, Commented Aug 22, 2013 at 19:53
DonA. I appreciate you looking through this but if you re-read my post I said it DOES compile, however, it DOESN'T when the 2 lines are moved into the class, rather than the method. — Snik
– Snik, Commented Aug 22, 2013 at 20:20
Right, I mean what errors? I don't get any. Can you show us how you initialize this class? — OneFineDay
– OneFineDay, Commented Aug 22, 2013 at 20:52

Alberto · Accepted Answer · 2013-08-22 21:01:51Z

3

Of course you can initialize an jagged array, but the syntax is slightly different:

public class Place
{
    private string[][] places = new string[2][]
    {
        new string[] { "Canada", "United States" },
        new string[] { "Calgary", "Edmonton", "Toronto" },
    };

    public void enumerate()
    {
        Console.WriteLine(places[0][1]);
    }
}

answered Aug 22, 2013 at 21:01

Alberto

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3 Comments

Snik Over a year ago

Well, that solves that. Thank you. I'm still fuzzy on why this is a special case with arrays? And i'm not familiar with the syntax you used (encapsulating an array).

Alberto Over a year ago

It is simply the syntax for array declarations and initialization, some examples here

Snik Over a year ago

Thanks Alberto. I suppose that's just the way its done with arrays and I will get used to the syntax.

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