编程之美---阶乘末尾有几个"零"?(C#实现)

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

namespace ConsoleApplication1
{
    class Program
    {
        delegate long DoMath(long num);

        static void Main(string[] args)
        {
            Program p = new Program();
            p.GetFactorial(26);
            DoMath d = new DoMath(p.HowManyZero);
            d += p.HowManyZero2;
            d(26);
            Console.Read();
        }

        public long HowManyZero(long num) //第一种解法
        {
            long result = 0;
            for (long i = 1; i <= num; i++)
            {
                long j = i;
                while (j % 5 == 0)
                {
                    result++; //检查每一个数可以分解因式出多少个5
                    j /= 5;
                }
            }

            Console.WriteLine(result);
            return result;
        }

        public long HowManyZero2(long num) //第二种
        {
            long ret = 0;
            while (num != 0)
            {
                ret += num / 5; //可以被5整除，然后是25、125、625......
                num /= 5;
            }

            Console.WriteLine(ret);
            return ret;
        }

        public decimal GetFactorial(long num) //获得阶乘
        {
            decimal ret = 1;
            for (long i = 1; i <= num; i++)
            {
                ret *= i;
            }

            Console.WriteLine(ret);
            return ret;
        }
    }
}

书上只标了2颗星，我怎么觉得这么费劲….
PS：decimal都算不到30的阶乘啊……

具体讲解书上有

顺便复习一下delegate~~~~~~~