斐波那契数列 递归与非递归实现

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

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(Foo(10).ToString());
            Console.WriteLine(koop(100).ToString());
            Console.ReadLine();
        }

        public static int Foo(int i)
        {
            if (i < 3)
            {
                return 1;
            }
            else
            {
                return Foo(i - 1) + Foo(i - 2);
            }
        }

        public static long koop(int x)
        {
            long start = 1;
            long next = 1;
            long third =0 ;
            for (int i = 2; i < x; i++)
            {
                third = start + next;
                start = next;
                next = third;
            }
            return third;
        }

    }
}