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);
  }
}