Sample code sharing on how to implement WeChat red envelope function in C#

class Program
  {
    static void Main(string[] args)
    {
      //初始化要发起的红包基础数据
      double total = 100;
      int num = 50;
      double min = 0.01;
      string temp;
      bool flag = false;
      Console.WriteLine(string.Format("是否需要自定义红包金额和数量（默认{0}元/{1}人）Y/N：", total, num));
      temp = Console.ReadLine();
      if (temp.Trim().ToLower().Equals("y") || temp.Trim().ToLower().Equals("yes"))
      {
        Console.WriteLine("请输入你要发起的红包金额：");
        do
        {
          temp = Console.ReadLine();
          flag = double.TryParse(temp, out total);
          if (!flag)
          {
            Console.WriteLine("金额必须为整数或小数，请重新输入：");
          }
        } while (!flag);
        Console.WriteLine("请输入你要发起的红包个数：");
        do
        {
          temp = Console.ReadLine();
          flag = int.TryParse(temp, out num);
          if (!flag)
          {
            Console.WriteLine("红包个数必须为整数，请重新输入：");
          }
        } while (!flag);
      }

      total -= min * num;
      if (total < 0)
      {
        Console.WriteLine("抱歉，你的金额不足！");
        return;
      }

      //产生正态分布的随机红包金额，并计算相关的金额和数量保证数据的准确性
      double average = total / num;
      double variance = 1;
      Random u1 = new Random();
      Random u2 = new Random();
      double[] nums = new double[num];

      for (int i = 0; i < num; i++)
      {
        double? result = total;
        if (i < num - 1 && total > 0)
        {
          do
          {
            result = Round((double)Normal(u1.NextDouble(), u2.NextDouble(), average, variance), 2);
          } while (result == null || result < 0);
          if (total > result)
          {
            total = (double)Round((total - (double)result), 2);
          }
          else
          {
            result = total;
            total = 0;
          }
        }
        else if (i == num - 1)
        {
          total = 0;
        }
        nums[i] = Math.Round(min + (double)result, 2); //浮点运算问题，这里需要四舍五入数据才正确

        Console.WriteLine(string.Format("第{0}个红包金额：{1}", i + 1, (min + result)));
        Console.WriteLine("剩余金额：" + ((i != num - 1 && total == 0) ? min * (num - i - 1) : total + (min * (num - i - 1))));
      }
      Console.WriteLine("最大金额：" + nums.Max());
      Console.WriteLine("最小金额：" + nums.Min());
      Console.WriteLine("总额：" + Round(nums.Sum(), 2));
      Console.WriteLine("初始方差：" + variance);
      Console.WriteLine("结果方差：" + Variance(nums));
      Console.WriteLine("按任意键退出！");

      Console.ReadKey();
    }

    /// <summary>
    /// 产生符合正态分布的随机数
    /// </summary>
    /// <param name="u1">正态分布第一个随机数</param>
    /// <param name="u2">正态分布第二个随机数</param>
    /// <param name="averageValue">正态期望(平均值)</param>
    /// <param name="variance">正态标准差(Math.Sqrt(方差))</param>
    /// <returns></returns>
    public static double? Normal(double u1, double u2, double averageValue, double variance)
    {
      double? result = null;
      try
      {
        result = averageValue + Math.Sqrt(variance) * Math.Sqrt((-2) * Math.Log(u1)) * Math.Sin(2 * Math.PI * u2);
      }
      catch (Exception)
      {
        result = null;
      }

      return result;
    }

    /// <summary>
    /// 求一组数据的方差
    /// </summary>
    /// <param name="list">要求的数组</param>
    /// <returns></returns>
    public static double Variance(double[] nums)
    {
      double average = nums.Sum() / nums.Length;
      double sum = 0;
      double variance = 0;
      foreach (double num in nums)
      {
        sum += Math.Pow((num - average), 2);
      }
      variance = sum / nums.Length;

      return variance;
    }

    /// <summary>
    /// 截取小数指定小数位，且不四舍五入
    /// </summary>
    /// <param name="originNum">要截取的小数</param>
    /// <param name="lastNum">截取小数后位数</param>
    /// <returns></returns>
    public static double? Round(double originNum, int lastNum)
    {
      double? result = null;
      int index = originNum.ToString().IndexOf(&#39;.&#39;);
      if (index != -1)
      {
        string temp = originNum.ToString();
        result = Convert.ToDouble(temp.Substring(0, index + 1) + temp.Substring(index + 1, Math.Min(temp.Length - index - 1, lastNum)));
      }
      if (result == 0)
      {
        result = null;
      }
      else if (index == -1)
      {
        result = originNum;
      }

      return result;
    }
  }