What is IEnumerator

* Supports a simple iteration over a non-generic collection.
* IEnumerator is the base interface for all non-generic enumerators.
the IEnumerator provides two abstract methods and a property to pull a particular element in a collection. And they are Reset(), MoveNext() and Current.

*The foreach statement of the C# language (for each in Visual Basic) hides the complexity of the enumerators. Therefore, using foreach is recommended instead of directly manipulating the enumerator.

*Initially, the enumerator is positioned before the first element in the collection. You must call the MoveNext method to advance the enumerator to the first element of the collection before reading the value of Current; otherwise, Current is undefined.

The signature of IEnumerator members is as follows:

   void Reset()  ->method returns a void type and helps you to position the pointer just before the start point.
   public void Reset()
    {
        //Get total number of element in a collection
        length = slist.Count;

        //Setting the pointer to just before the beginning of collection
        current = -1;
    }

   bool MoveNext() ->method will help you to position the location of the required element in the collection while sending a flag value.

public bool MoveNext()
{
//this will increment the counter variable
//and will check whether it is exceeding the actual length of our collection
return(++current<length);
}

   object Current  ->property of IEnumerator interface will return an individual element of a given collection.

Example:

using System;
/// <summary>
/// Implementation of Singleton Pattern
/// </summary>
using System.Collections;

// Simple business object.
public class Person
{
    public Person(string fName, string lName)
    {
        this.firstName = fName;
        this.lastName = lName;
    }

    public string firstName;
    public string lastName;
}

// Collection of Person objects. This class
// implements IEnumerable so that it can be used
// with ForEach syntax.
public class People : IEnumerable
{
    private Person[] _people;
    public People(Person[] pArray)
    {
        _people = new Person[pArray.Length];

        for (int i = 0; i < pArray.Length; i++)
        {
            _people[i] = pArray[i];
        }
    }

    // Implementation for the GetEnumerator method.
    IEnumerator IEnumerable.GetEnumerator()
    {
        return (IEnumerator)GetEnumerator();
    }

    public PeopleEnum GetEnumerator()
    {
        return new PeopleEnum(_people);
    }
}

// When you implement IEnumerable, you must also implement IEnumerator.
public class PeopleEnum : IEnumerator
{
    public Person[] _people;

    // Enumerators are positioned before the first element
    // until the first MoveNext() call.
    int position = -1;

    public PeopleEnum(Person[] list)
    {
        _people = list;
    }

    public bool MoveNext()
    {
        position++;
        return (position < _people.Length);
    }

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

    object IEnumerator.Current
    {
        get
        {
            return Current;
        }
    }

    public Person Current
    {
        get
        {
            try
            {
                return _people[position];
            }
            catch (IndexOutOfRangeException)
            {
                throw new InvalidOperationException();
            }
        }
    }
}

class Program
{
    static void Main()
    {
        Person[] peopleArray = new Person[3]
        {
            new Person("John", "Smith"),
            new Person("Jim", "Johnson"),
            new Person("Sue", "Rabon"),
        };

        People peopleList = new People(peopleArray);
        foreach (Person p in peopleList)
            Console.WriteLine(p.firstName + " " + p.lastName);

    }

}