生成四位隨機數，用于登錄驗證碼制作。

兩種方法，調用其一即可：

 1 using System; 2 using System.Collections.Generic; 3 using System.Linq; 4 using System.Text; 5 using System.Threading.Tasks; 6  7 namespace SJ_random 8 { 9     class Class_main10     {11         static void Main()12         {13             Class_random rdm = new Class_random();14 15             Random rm = new Random();16 17             string s = string.Empty;                //置空字符串.18 19             Console.WriteLine(rdm.random_1(s, rm)); //調用方法 random_1 ，產生隨機數.20 21             Console.Write(rdm.random_2(s, rm));     //調用方法 random_2 ，產生隨機數.22 23             Console.ReadKey();24         }25     }26 27     public class Class_random28     {29         /// <summary>30         /// 方法一，生成隨機數。31         /// </summary>32         /// <param name="s">接收生成的隨機數</param>33         /// <param name="rm">random的實例</param>34         /// <returns>生成的隨機數</returns>35         public string random_1(string s, Random rm)36         {37             for (int i = 0; i < 4; i++)38             {39                 int k = rm.Next();40 41                 char j = (char)('0' + (char)(k % 10));42 43                 s += j.ToString();44             }45             return s;46         }47 48         /// <summary>49         /// 方法二，生成隨機數。50         /// </summary>51         /// <param name="s">接收生成的隨機數</param>52         /// <param name="rm">random的實例</param>53         /// <returns>生成的隨機數</returns>54         public string random_2(string s, Random rm)55         {56             s = Convert.ToString(rm.Next(1000, 9999));57 58             return s;59         }60     }61 }