Initializing an Array of Structs in C#

Firstly, do you really have to have a mutable struct? They're almost always a bad idea. Likewise public fields. There are some very occasional contexts in which they're reasonable (usually both parts together, as with ValueTuple) but they're pretty rare in my experience.

Other than that, I'd just create a constructor taking the two bits of data:

class SomeClass
{

    struct MyStruct
    {
        private readonly string label;
        private readonly int id;

        public MyStruct (string label, int id)
        {
            this.label = label;
            this.id = id;
        }

        public string Label { get { return label; } }
        public string Id { get { return id; } }

    }

    static readonly IList<MyStruct> MyArray = new ReadOnlyCollection<MyStruct>
        (new[] {
             new MyStruct ("a", 1),
             new MyStruct ("b", 5),
             new MyStruct ("q", 29)
        });
}

Note the use of ReadOnlyCollection instead of exposing the array itself - this will make it immutable, avoiding the problem exposing arrays directly. (The code show does initialize an array of structs - it then just passes the reference to the constructor of ReadOnlyCollection<>.)

Are you using C# 3.0? You can use object initializers like so:

static MyStruct[] myArray = 
            new MyStruct[]{
                new MyStruct() { id = 1, label = "1" },
                new MyStruct() { id = 2, label = "2" },
                new MyStruct() { id = 3, label = "3" }
            };

You cannot initialize reference types by default other than null. You have to make them readonly. So this could work;

    readonly MyStruct[] MyArray = new MyStruct[]{
      new MyStruct{ label = "a", id = 1},
      new MyStruct{ label = "b", id = 5},
      new MyStruct{ label = "c", id = 1}
    };

Change const to static readonly and initialise it like this

static readonly MyStruct[] MyArray = new[] {
    new MyStruct { label = "a", id = 1 },
    new MyStruct { label = "b", id = 5 },
    new MyStruct { label = "q", id = 29 }
};

I'd use a static constructor on the class that sets the value of a static readonly array.

public class SomeClass
{
   public readonly MyStruct[] myArray;

   public static SomeClass()
   {
      myArray = { {"foo", "bar"},
                  {"boo", "far"}};
   }
}