菊池さん考案のフィボナッチ数列なIEnumerable<int>を返す関数

Program.cs

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

namespace FibonacciSequence
{
  class Program
  {
    static void Main(string[] args)
    {
      var i = 0;
      foreach (var fib in Fib().Take(11))
      {
        Console.WriteLine(i + ":" + fib);

        i++;
      }
    }

    private static IEnumerable<int> Fib()
    {
      var a = 0;
      var b = 1;
      yield return a;
      yield return b;
      for (; ; )
      {
        a = a + b;
        yield return a;
        b = a + b;
        yield return b;
      }
    }
  }
}