using System;

public class Test
{
	public static void Main()
	{
		    string[] A = new string[] { "A", "B", "C", "D" };
            string[] B = new string[A.Length * 2 + 2]; // you wanted to add something other as well
            for (int i = 1; (i-1) / 2 < A.Length; i += 2)
            {
                B[i] = A[(i-1) / 2];
            }
            
            for(int i=0; i<B.Length;i++)
                Console.WriteLine("Index: {0} Value: {1}", i, B[i]);
	}
}