写个函数C# 生成20位0-9A-Z字符串

你可以使用以下代码来生成一个20位的0-9A-Z字符串：

using System;
using System.Text;

public class Program
{
    public static void Main()
    {
        string randomString = GenerateRandomString(20);
        Console.WriteLine(randomString);
    }

    public static string GenerateRandomString(int length)
    {
        const string chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        StringBuilder stringBuilder = new StringBuilder(length);

        Random random = new Random();
        for (int i = 0; i < length; i++)
        {
            int index = random.Next(chars.Length);
            stringBuilder.Append(chars[index]);
        }

        return stringBuilder.ToString();
    }
}

运行这个程序，它将输出一个随机生成的20位字符串，包含数字和大写字母