Yield Keyword C# with IEnumerable

Used in an iterator block to provide a value to the enumerator object or to signal the end of iteration.

expression is evaluated and returned as a value to the enumerator object; expressionhas to be implicitly convertible to the yield type of the iterator.

The yield statement can only appear inside an iterator block, which might be used as a body of a method, operator, or accessor. The body of such methods, operators, or accessors is controlled by the following restrictions:

• Unsafe blocks are not allowed.
• Parameters to the method, operator, or accessor cannot be ref or out.

A yield statement cannot appear in an anonymous method. For more information, seeAnonymous Methods (C# Programming Guide).

When used with expression, a yield return statement cannot appear in a catch block or in a try block that has one or more catch clauses. For more information, seeException Handling Statements (C# Reference).

using System;

using System.Collections.Generic;

public class MyClass

{

    public static  IEnumerable<int> Powers(int from,int to)

    {

        for (int i = from; i <= to; ++i)

        {

            yield return (int)Math.Pow(2, i);

        }

    }

    static void Main()

    {

        IEnumerable<int> powers = Powers(0, 16);

        foreach (int result in powers)

        {

            Console.WriteLine(result);

        }

    }

}

Source :MSDN