C# Program to Implement for-each in Interface

/*
 * C# Program to Implement for-each in Inteface
 */
using System;
using System.Collections;
class GrowableArray : IEnumerable
{
  object[] a;
  public GrowableArray(int size) 
  {
    a = new object[size];
  }
  public GrowableArray() : this(8) {}
  void Grow() 
  {
    object[] b = new object[2 * a.Length];
    Array.Copy(a, b, a.Length);
    a = b;
  }
  public object this[int i] 
  {
    set 
    {
      if (i >= a.Length) Grow();
      a[i] = value;
    }
    get 
    {
      if (i >= a.Length) Grow();
      return a[i];
    }
  }
  public IEnumerator GetEnumerator() 
  {
    return new GAEnumerator(a);
  }
  class GAEnumerator : IEnumerator 
  {
    object[] a;
    int i = -1;
    public GAEnumerator(object[] a) { this.a = a; }
    public object Current 
   { 
      get 
      { 
         return a[i]; 
      }
   }
    public void Reset() 
    { 
        i = -1; 
    }
    public bool MoveNext() 
    { 
      do i++; 
      while (i < a.Length && a[i] == null);
      if (i == a.Length) 
         return false; 
      else return true;
    }
  }
}
class Test 
{
public static void Main() 
{
    GrowableArray a = new GrowableArray(2);
    a[0] = 0;
    a[1] = 1;
    a[3] = 3;
    foreach (object x in a) Console.Write(" " + x);
}
}