using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace SJ_random {     class Class_main     {         static void Main()         {             Class_random rdm = new Class_random();             Random rm = new Random();             string s = string.Empty;                //置空字符串.             Console.WriteLine(rdm.random_1(s, rm)); //调用方法 random_1 ，产生随机数.             Console.Write(rdm.random_2(s, rm));     //调用方法 random_2 ，产生随机数.             Console.ReadKey();         }     }     public class Class_random     {         /// <summary>         /// 方法一，生成随机数。         /// </summary>         /// <param name="s">接收生成的随机数</param>         /// <param name="rm">random的实例</param>         /// <returns>生成的随机数</returns>         public string random_1(string s, Random rm)         {             for (int i = 0; i < 4; i++)             {                 int k = rm.Next();                 char j = (char)('0' + (char)(k % 10));                 s += j.ToString();             }             return s;         }         /// <summary>         /// 方法二，生成随机数。         /// </summary>         /// <param name="s">接收生成的随机数</param>         /// <param name="rm">random的实例</param>         /// <returns>生成的随机数</returns>         public string random_2(string s, Random rm)         {             s = Convert.ToString(rm.Next(1000, 9999));             return s;         }     } }