求1+2!+3!+...+20!的和

Question

求1+2!+3!+...+20!的和

Answer 1

//求n的阶乘        private static int CalJieCheng(int n)
        {
            if (n < 0)
            {
                throw new Exception("请示输入正整数！");
            }
            if (n < 2)
            {
                return 1;
            }
            else if (n > 16)
            {
                string text = string.Format("结果超出int32的范围：{0}，无法显示！",int.MaxValue.ToString());
                throw new Exception(text);
            }
            else
            {
                return n * Run(n - 1);
            }        }        private static int Run(int m)
        {
            if (m == 1)
            {
                return 1;
            }
            return m * Run(m - 1);
        }        static void Main(string[] args)
        {
            while (true)
            {
                Console.WriteLine("请输入正整数：");
                string s = Console.ReadLine();
                int n = int.Parse(s);
                int reslut = CalJieCheng(n);
                Console.WriteLine(s + "的阶乘是：" + reslut.ToString());
            }
        }