Do While 循环中的随机数

Question

我一直在尝试用字母数字字符创建一个随机字符串，并使用 Do-While 循环来检查随机字符串是否符合要求。否则，它应该继续执行循环。但是，我发现我总是一遍又一遍地生成相同的字符串的代码。为了演示，我设置了int message_length = 2 并要求While Loop 检查生成的字符串是否为“ab”，如while (check != "ab")。

我尝试将Random seed = new Random() 放在 Do 循环中，在 Do 循环之外，在 Main() 之外，你可以看到我注释掉的代码。他们都没有工作。我使用了 Visual Studio 2017、Windows 10 家庭版。任何人都可以帮忙吗？非常感谢！

(Further cmets: 虽然我现在的代码工作正常，但我仍然不明白为什么在这种情况下原行 check = all_message.ToString(); 可以中断随机数生成器。恕我直言，while 条件 while (check != "ab") 仍然是 True所以循环将继续进行。但是为什么随机数生成器停止生成新种子？任何人都可以分享这方面的知识吗？

using System;
using System.Text;
using System.Collections.Generic;


public class Program
{
    //static Random seed = new Random();

    public static void Main(string[] arggs)
    {
        Random seed = new Random();
        const string src = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        Console.WriteLine(src.Length);
        int string_length = 2;
        List<string> all_message = new List<string>();
        string check = "";
        do
        {
            //Random seed = new Random();
            int i = 0;
            StringBuilder message = new StringBuilder();
            for (int j = 0; j < string_length; j++)
            {
                char c = src[seed.Next(0, src.Length)];
                message.Append(c);
            }
            all_message.Add(message.ToString());
            check = all_message.ToString();
            Console.WriteLine(i + " = " + all_message[i]);

            i++;
        }
        while (check != "ab");

    }
}

Answer 1

在其他人的帮助下，我找到了问题所在。关键更改是check = string.Join("", all_message.ToArray());。几乎没有其他小的改动，解决方案就在这里：

using System;
using System.Text;
using System.Collections.Generic;


public class Program
{
    //static Random seed = new Random();

    public static void Main(string[] arggs)
    {
        Random seed = new Random();
        const string src = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        Console.WriteLine(src.Length);
        int string_length = 2;
        string check = "";
        int i = 0;
        do
        {
            //Random seed = new Random();
            List<string> all_message = new List<string>();

            StringBuilder message = new StringBuilder();
            for (int j = 0; j < string_length; j++)
            {
                char c = src[seed.Next(0, src.Length)];
                message.Append(c);
            }
            all_message.Add(message.ToString());
            check = string.Join("", all_message.ToArray());
            //Console.WriteLine(check);
            Console.WriteLine(i + " = " + check);

            i++;
        }
        while (check != "ab");

    }
}

Answer 2

我运行了以下内容：

Random seed = new Random();
const string src = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
Console.WriteLine(src.Length);
int string_length = 2;
List<string> all_message = new List<string>();
string check = "";
int i = 0;
do
{
    //Random seed = new Random();
    
    StringBuilder message = new StringBuilder();
    for (int j = 0; j < string_length; j++)
    {
        char c = src[seed.Next(0, src.Length)];
        message.Append(c);      
    }   
    all_message.Add(message.ToString());
    check = all_message.ToString();
    Console.WriteLine(i + " = " + all_message[i]);
    i++;
}
while (i < 3);

我的输出是：

62
0 = PQ
1 = xw
2 = he

请注意，索引 i 在循环外初始化，因此不会每次都重置。

那么问题就变成了，您的要求是什么，何时终止循环以及check 应该是什么？

Answer 3

您将在循环的每次迭代中重置计数器“i”，因此您将始终将生成列表的第一个元素写入控制台。在循环外初始化 i。

Answer 4

提示：阅读 cmets。

        Random seed = new Random();
        const string src = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        Console.WriteLine(src.Length);
        int string_length = 2;
        List<string> all_message = new List<string>();
        string check = "";
        do
        {
            //Random seed = new Random(); -- you do not need it any more hier.

            int i = 0; // if you whant counting with i, put it above the do while.

            StringBuilder message = new StringBuilder();

            for (int j = 0; j < string_length; j++)
            {
                char c = src[seed.Next(0, src.Length)];
                message.Append(c);
            }


            all_message.Add(message.ToString());

            check = all_message.ToString(); // this is the list from string you do not need it realy and list to string  = System.Collections.Generics.List....
            //instead check should be equal to all_message[i] case i counting properly

            Console.WriteLine(i + " = " + all_message[i]); // and hier simply print the check, you allready have the value.

            i++;
        }
        while (check != "ab");