using System;
using System.Collections;

public class Starter {
    public static void Main() {
        SimpleCollection simple = new SimpleCollection(new object[] { 1, 2, 3, 4, 5, 6, 7 });
        IEnumerator enumerator = simple.GetEnumerator();
        while (enumerator.MoveNext()) {
            Console.WriteLine(enumerator.Current);
        }
    }
}

public class SimpleCollection : IEnumerable {
    public SimpleCollection(object[] array) {
        items = array;
    }
    public IEnumerator GetEnumerator() {
        return new Enumerator(items);
    }

    private object[] items = null;
}
public class Enumerator : IEnumerator {
    public Enumerator(object[] items) {
        elements = new object[items.Length];
        Array.Copy(items, elements, items.Length);
        cursor = -1;
    }
    public bool MoveNext() {
        ++cursor;
        if (cursor > (elements.Length - 1)) {
            return false;
        }
        return true;
    }
    public void Reset() {
        cursor = -1;
    }
    public object Current {
        get {
            if (cursor > (elements.Length - 1)) {
                throw new InvalidOperationException("Enumeration already finished");
            }
            if (cursor == -1) {
                throw new InvalidOperationException(
                    "Enumeration not started");
            }
            return elements[cursor];
        }
    }

    private int cursor;
    private object[] elements = null;
}
    

   
 

using System;
using System.Collections;
public class SimpleCollection : IEnumerable {

    public SimpleCollection(object[] array) {
        items = array;
    }

    public IEnumerator GetEnumerator() {
        return new Enumerator(this);
    }

    private class Enumerator : IEnumerator {

        public Enumerator(SimpleCollection obj) {
            oThis = obj;
            cursor = -1;
        }

        public bool MoveNext() {
            ++cursor;
            if (cursor > (oThis.items.Length - 1)) {
                return false;
            }
            return true;
        }


        public void Reset() {
            cursor = -1;
        }

        public object Current {
            get {
                if (cursor > (oThis.items.Length - 1)) {
                    throw new InvalidOperationException(

                        "Enumeration already finished");
                }
                if (cursor == -1) {
                    throw new InvalidOperationException(
                        "Enumeration not started");
                }
                return oThis.items[cursor];
            }
        }

        private int cursor;
        private SimpleCollection oThis;
    }


    private object[] items = null;
}

    

using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;

public class Primes {
private long min;
private long max;

public Primes(long minimum, long maximum) {
min = minimum;
max = maximum;
}

public IEnumerator GetEnumerator() {
for (long possiblePrime = min; possiblePrime <= max; possiblePrime++) { bool isPrime = true; for (long possibleFactor = 2; possibleFactor <= (long)Math.Floor(Math.Sqrt(possiblePrime)); possibleFactor++) { long remainderAfterDivision = possiblePrime % possibleFactor; if (remainderAfterDivision == 0) { isPrime = false; break; } } if (isPrime) { yield return possiblePrime; } } } } class Program { static void Main(string[] args) { Primes primesFrom2To1000 = new Primes(2, 1000); foreach (long i in primesFrom2To1000) Console.Write("{0} ", i); } } [/csharp]

using System;
using System.Collections.Generic;

public class Starter {
public static void Main() {
MyClass obj = new MyClass();
foreach (int item in obj) {
Console.Write(item);
}
}
}

public class MyClass {

private int[] list1 = new int[] { 0, 2, 4, 6, 8 };
private int[] list2 = new int[] { 1, 3, 5, 7, 9 };

public IEnumerator GetEnumerator() {
for (int index = 0; index < 4; ++index) { yield return list1[index]; yield return list2[index]; } } } [/csharp]

   
 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class Tree<TItem> : IEnumerable<TItem> where TItem : IComparable<TItem> {
    public Tree(TItem nodeValue) {
        this.NodeData = nodeValue;
        this.LeftTree = null;
        this.RightTree = null;
    }

    public void Insert(TItem newItem) {
        TItem currentNodeValue = this.NodeData;
        if (currentNodeValue.CompareTo(newItem) > 0) {
            if (this.LeftTree == null) {
                this.LeftTree = new Tree<TItem>(newItem);
            } else {
                this.LeftTree.Insert(newItem);
            }
        } else {
            if (this.RightTree == null) {
                this.RightTree = new Tree<TItem>(newItem);
            } else {
                this.RightTree.Insert(newItem);
            }
        }
    }

    public void WalkTree() {
        if (this.LeftTree != null) {
            this.LeftTree.WalkTree();
        }

        Console.WriteLine(this.NodeData.ToString());

        if (this.RightTree != null) {
            this.RightTree.WalkTree();
        }
    }

    public TItem NodeData { get; set; }
    public Tree<TItem> LeftTree { get; set; }
    public Tree<TItem> RightTree { get; set; }


    IEnumerator<TItem> IEnumerable<TItem>.GetEnumerator() {
        return new TreeEnumerator<TItem>(this);
    }
    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {
        throw new NotImplementedException();
    }


}

class TreeEnumerator<T> : IEnumerator<T> where T : IComparable<T> {
    public TreeEnumerator(Tree<T> data) {
        this.currentData = data;
    }

    private void populate(Queue<T> enumQueue, Tree<T> tree) {
        if (tree.LeftTree != null) {
            populate(enumQueue, tree.LeftTree);
        }

        enumQueue.Enqueue(tree.NodeData);

        if (tree.RightTree != null) {
            populate(enumQueue, tree.RightTree);
        }
    }

    private Tree<T> currentData = null;
    private T currentItem = default(T);
    private Queue<T> enumData = null;

    T IEnumerator<T>.Current {
        get {
            if (this.enumData == null)
                throw new InvalidOperationException("Use MoveNext before calling Current");

            return this.currentItem;
        }
    }
    void IDisposable.Dispose() {
        // throw new NotImplementedException();
    }
    object System.Collections.IEnumerator.Current {
        get { throw new NotImplementedException(); }
    }
    bool System.Collections.IEnumerator.MoveNext() {
        if (this.enumData == null) {
            this.enumData = new Queue<T>();
            populate(this.enumData, this.currentData);
        }

        if (this.enumData.Count > 0) {
            this.currentItem = this.enumData.Dequeue();
            return true;
        }
        return false;
    }
    void System.Collections.IEnumerator.Reset() {
        throw new NotImplementedException();
    }
}

class Program {
    static void Main(string[] args) {
        Tree<int> tree1 = new Tree<int>(10);
        tree1.Insert(5);
        tree1.Insert(11);
        tree1.Insert(5);
        tree1.Insert(-12);
        tree1.Insert(15);
        tree1.Insert(0);
        tree1.Insert(14);
        tree1.Insert(-8);
        tree1.Insert(10);

        foreach (int item in tree1)
            Console.WriteLine(item);
    }
}

    

   
 

using System;
using System.Collections;

public class Starter {
    public static void Main() {
        MyCollection simple = new MyCollection(new object[] { 1, 2, 3, 4, 5, 6, 7 });
        IEnumerator enumerator = simple.GetEnumerator();
        enumerator.MoveNext();
        Console.WriteLine(enumerator.Current);
        enumerator.MoveNext();
        simple[4] = 10;
        Console.WriteLine(enumerator.Current);
        enumerator.MoveNext();
    }
}

public class MyCollection : IEnumerable {
    public MyCollection(object[] array) {
        items = array;
        version = 1;
    }
    public object this[int index] {
        get {
            return items[index];
        }
        set {
            ++version;
            items[index] = value;
        }
    }

    public IEnumerator GetEnumerator() {
        return new Enumerator(this);
    }

    private class Enumerator : IEnumerator {

        public Enumerator(MyCollection obj) {
            oThis = obj;
            cursor = -1;
            version = oThis.version;
        }

        public bool MoveNext() {
            ++cursor;
            if (cursor > (oThis.items.Length - 1)) {
                return false;
            }
            return true;
        }
        public void Reset() {
            cursor = -1;
        }

        public object Current {
            get {
                if (oThis.version != version) {
                    throw new InvalidOperationException("Collection was modified");
                }
                if (cursor > (oThis.items.Length - 1)) {
                    throw new InvalidOperationException("Enumeration already finished");
                }
                if (cursor == -1) {
                    throw new InvalidOperationException("Enumeration not started");
                }
                return oThis.items[cursor];
            }
        }

        private int version;
        private int cursor;
        private MyCollection oThis;
    }
    private object[] items = null;
    private int version;
}

    

   
 

using System;
using System.Collections.Generic;
using System.Linq;
public class MainClass {
    public static void Main() {

        IEnumerable<char> query = "Not what you might expect";

        foreach (char vowel in "aeiou")
            query = query.Where(c => c != vowel);

        foreach (char c in query) Console.Write(c); 
    }
}