一个洗牌程序算法，随机交换位置

 int[] numbers=new int [20];     //建立一个数组
            Random rand=new Random (); //生成随机数
            string result="";                    //保存结果
            for (int i = 0; i < 20; i++)       //初始化数组
                numbers[i] = i+1;
            for (int i = 0; i < 20; i++)          //洗牌
              {
                int temp = rand.Next(20);
                int tempNumber = numbers[i ];
                numbers[i] = numbers[temp ];
                numbers[temp] =tempNumber ;
              }
            for (int i = 0; i < 4; i++)          //这个用来排列你想要的那4个数
                for (int j = 0; j < 4; j++)         
                {                                           //你不需要就去掉它
                    int temp;
                    if (numbers[i] < numbers[j])
                    {
                        temp = numbers[j];
                        numbers[j] = numbers[i];
                        numbers[i] = temp;
                    }
                    else
                        continue;
                }                                         //生成结果项
                    for (int i = 0; i < 4; i++)
                        result += "result" + i.ToString() + "==>" + numbers[i].ToString() + Environment.NewLine;
                      MessageBox.Show(result );     //输出结果