Program to Implement for-each in Inteface

/*
 * 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);
}
}