using System;
using System.Collections;
namespace Wrox.ProCSharp.Arrays
{
public class HelloCollection{
public IEnumerator < string > GetEnumerator()
{
yield return "Hello";
yield return "World";
}
}

===============


public void HelloWorld()
{
var helloCollection = new HelloCollection();
foreach (var s in helloCollection)
{
Console.WriteLine(s);
}
}
}


====================


public class HelloCollection
{
public IEnumerator GetEnumerator()
{
return new Enumerator(0);

// What and does this statement does
// Also how does PROBABLY case value 0 goes to get to 1 and 2 and break:
// the break is mandatory , but is a fallthrough allowed
}
public class Enumerator: IEnumerator<string>, IEnumerator, IDisposable
{
private int state;
private string current;
public Enumerator(int state)
{
this.state = state;
}
bool System.Collections.IEnumerator.MoveNext()
{
switch (state)
{
case 0:
current = "Hello";
state = 1;
return true;
case 1:
current = "World";
state = 2;
return true;
case 2:
break;
}
return false;
}
void System.Collections.IEnumerator.Reset()
{
throw new NotSupportedException();

//Why so?
string System.Collections.Generic.IEnumerator<string>.Cur rent
{
get
{
return current;
}
}
object System.Collections.IEnumerator.Current
{
get
{
return current;
}
}
void IDisposable.Dispose()

//why So?{
}
}


Why are 2 classes names the same HelloCollection?

The text between the code lines should answer this. The first two code blocks you've in your post are the ones you can write. The 2nd HelloCollection shows the code as it is created from the C# compiler out of the yield statements.

Regarding your inline questions in the code:
With a switch statement you can either do a break, a goto (explicit fallthrough), or a return. The generated code does a return, and thus neither a break nor a fallthrough.

Hope this helps.

__________________
Christian
CN innovation
Visit my blog at: csharp.christiannagel.com
Follow me on twitter: @christiannagel

Hello Teacher
This is my first letter to you
I just cannot believe that it is you who answered my query.
Thank you very much teacher ---
- well very often than not I will disturb this forum from now on
Regards
amigo1

oops I just forgot this

public class Enumerator: IEnumerator<string>, IEnumerator, IDisposable

As IEnumerator<string> is derived from IEnumerator and IDisposable, is it mandatory to inherit them too here in this case .

You're welcome :-)

It's not necessary to derive from the other interfaces, as this is done implicitly by the IEnumerator<string> interface. It is necessary to implement all the members of IEnumerator and IDisposable in both cases, if you explicitly derive from these interfaces, or if you implicitly derive from these interfaces by deriving from IEnumerable<string>.

__________________
Christian
CN innovation
Visit my blog at: csharp.christiannagel.com
Follow me on twitter: @christiannagel

thank you very much