public class FibonacciSequence : IEnumerable<int>
{
    private readonly int _numberOfValues;

    public FibonacciSequence(int numberOfValues)
    {
        _numberOfValues = numberOfValues;
    }

    public IEnumerator<int> GetEnumerator()
    {
        return new FibonacciEnumerator(_numberOfValues);
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

public class FibonacciEnumerator : IEnumerator<int>
{
    private readonly int _numberOfValues;
    private int _currentPosition;
    private int _currentTotal;
    private int _previousTotal;

    public FibonacciEnumerator(int numberOfValues)
    {
        _numberOfValues = numberOfValues;
    }

    public void Dispose()
    {
        GC.SuppressFinalize(this);
    }

    public bool MoveNext()
    {
        if (_currentPosition == 0)
        {
            _currentTotal = 1;
        }
        else
        {
            int newTotal = _previousTotal + _currentTotal;
            _previousTotal = _currentTotal;
            _currentTotal = newTotal;
        }
        _currentPosition++;
        return _currentPosition <= _numberOfValues;
    }

    public void Reset()
    {
        _currentPosition = 0;
        _currentTotal = 0;
        _previousTotal = 0;
    }

    public int Current
    {
        get { return _currentTotal; }
    }

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

 [Test]
 public void CanForEachEnumerable()
 {
    var fib = new FibonacciSequence(10);
    foreach (var num in fib)
    {
        Console.WriteLine(num);
    }

 }

{
    private readonly string _startingPath;

    public MP3Locator(string startingPath)
    {
        _startingPath = startingPath;
    }

    public IEnumerator<FileInfo> GetEnumerator()
    {
        return new MP3Enumerator(_startingPath);
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

public class MP3Enumerator : IEnumerator<FileInfo>
{
    private readonly IEnumerator<string> _fileEnumerator;
    private readonly string _startingPath;

    public MP3Enumerator(string startingPath)
    {
        _startingPath = startingPath;
        IEnumerable<string> file = Directory.EnumerateFiles(_startingPath, "*.*", SearchOption.AllDirectories);
        _fileEnumerator = file.GetEnumerator();
    }

    public void Dispose()
    {
        _fileEnumerator.Dispose();
    }

    public bool MoveNext()
    {
        return _fileEnumerator.MoveNext();
    }

    public void Reset()
    {
        _fileEnumerator.Reset();
    }

    public FileInfo Current
    {
        get { return new FileInfo(_fileEnumerator.Current); }
    }

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

[Test]
public void EnumateDirector()
{
    var files = new MP3Locator("D:\\LearningVedio");
    foreach (var file in files)
    {
        Console.WriteLine(file.Name);
        Console.WriteLine(file.Extension);
        Console.WriteLine(file.DirectoryName);
    }
}