C# 表达式体方法 C#算阶乘

        //表达式体方法private int Add(int a, int b) => a + b;

        [Fact]public void Test(){var result1 = Factorial(1);//1var result2 = Factorial(2);//2var result3 = Factorial(3);//6var result4 = Factorial(4);//24var result5 = Factorial(5);//120var result6 = Add(100, 200);//300Console.WriteLine("result6：{0}", result6);var result7 = Math.Abs(123.456);var result8 = Math.Abs(-123.456);var reportId = string.Concat("VWFS_OnePage3.0_AFC", string.Format("{0:d8}", new Random().Next(10000000, 99999999)));var s = "123.456";var result9 = s.PadLeft(6);//123.456var result10 = s.PadLeft(6, '#');//123.456var result91 = s.Length == result9.Length;var result101 = s.Length == result10.Length;var result11 = s.Insert(4, "200#");//123.200#456s = "abcdefabcdef";var result12 = s[0];var result13 = s[s.Length - 1];var result14 = s.IndexOf("c");var result15 = s.LastIndexOf("c");var result16 = result14 == result15;var result17 = new int[,] { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };var result18 = new int[3][];result18[0] = new int[] { 1, 2, 3 };result18[1] = new int[] { 3, 4, 5 };result18[2] = new int[] { 7, 8, 9, 10 };//result18[3] = new int[] { 11, 12, 13, 14 };var result19 = DateTime.Now.Ticks;//638279743914331688}

        private int Factorial(int n){if (n == 0)return 1;elsereturn n * Factorial(n - 1);}

阶乘：

阶乘是基斯顿·卡曼(Christian Kramp，1760～1826)于 1808 年发明的运算符号，是数学术语。
一个正整数的阶乘(factorial)是所有小于及等于该数的正整数的积，并且0的阶乘为1。自然数n的阶乘写作n!。1808年，基斯顿·卡曼引进这个表示法。
亦即n!=1×2×3×...×(n-1)×n。阶乘亦可以递归方式定义：0!=1，n!=(n-1)!×n。