变量不会在目前的情况下是否存在？ [英] Variable does not exist in the current context?

问题描述

我知道这是最有可能是愚蠢的问题，但我是一个大学生谁是新的C＃和面向对象编程。我试图在别处找到了答案，但我没能找到任何可能的帮助。调试器不断告诉我该变量CUST_NUM不会在目前的情况下存在。如果有人能告诉我什么，我做错了，让我觉得自己像个白痴，我将不胜感激。 ！谢谢

 字符串get_cust_num（）
 {
布尔cust_num_valid = FALSE; （！cust_num_valid）
 
在
 {
 cust_num_valid = TRUE; 
 Console.Write（请输入客户编号：）; 
串CUST_NUM =到Console.ReadLine（）; 
 
如果（CUST_NUM ==000000||！Regex.IsMatch（CUST_NUM，@^ [0-9] + $）|| cust_num.Length！= 6）
 {
 cust_num_valid = FALSE; 
 Console.WriteLine（无效的客户编号检测到的顾客数必须是6位正整数（零无效））; 
} 
} 
 
返回CUST_NUM; 
} 
  

解决方案

在C＃中每个变量是存在内的范围的是由大括号定义的：

  {
 ... 
 INT X = 0; 
 ... 
 X = X + 1; //<  - 法律
 ... 
 //<  -  x被定义到这里
} 
 
 X = X  -  1; //<  - 非法的，提供没有其他的X，宣布
  

在你的情况， CUST_NUM 是限制而{...} 。它想什么价值应该代码的回报，如果的 cust_num_valid = TRUE 的，有没有
的 CUST_NUM 的都没有。

 而
 {//<（cust_num_valid！）;  -  CUST_NUM范围开始
 cust_num_valid = TRUE; 
 Console.Write（请输入客户编号：）; 
串CUST_NUM =到Console.ReadLine（）; 
 
如果（CUST_NUM ==000000||！Regex.IsMatch（CUST_NUM，@^ [0-9] + $）|| cust_num.Length！= 6）
 {
 cust_num_valid = FALSE; 
 Console.WriteLine（无效的客户编号检测到的顾客数必须是6位正整数（零无效））; 
} 
} //<  -  CUST_NUM范围结束
 
返回CUST_NUM; //<  - 出范围
的 

要修复你的代码放在字符串CUST_NUM =; 的 的外，而：

 字符串CUST_NUM =; //<  - （！cust_num_valid）声明
 
在
 {
 cust_num_valid = TRUE; 
 Console.Write（请输入客户编号：）; 
 CUST_NUM =到Console.ReadLine（）; //<  - 没有新的声明：串被删除
 
如果（CUST_NUM ==000000|| Regex.IsMatch（CUST_NUM，@^ [0-9] + $ ！）|| cust_num.Length = 6）
 {
 cust_num_valid = FALSE; 
 Console.WriteLine（无效的客户编号检测到的顾客数必须是6位正整数（零无效））; 
} 
} 
 
返回CUST_NUM; 
  

I know this is most likely a stupid question but I am a university student who is new to C# and object-oriented programming. I have tried to find the answer elsewhere but I wasn't able to find anything that could help. The debugger keeps telling me that the variable 'cust_num does not exist in the current context'. If someone can tell me what I have done wrong and make me feel like an idiot, I would greatly appreciate it. Thanks!

    string get_cust_num()
    {
        bool cust_num_valid = false;

        while (!cust_num_valid)
        {
            cust_num_valid = true;
            Console.Write("Please enter customer number: ");
            string cust_num = Console.ReadLine();

            if (cust_num == "000000" || !Regex.IsMatch(cust_num, @"^[0-9]+$") || cust_num.Length != 6)
            {
                cust_num_valid = false;
                Console.WriteLine("Invalid customer number detected. Customer numbers must be a 6 digit positive integer (zeros will not work)");
            }
        }

        return cust_num;
    }

解决方案

Each variable in C# is exists within a scope which is defined by curly braces:

{ 
  ...
  int x = 0;
  ...
  x = x + 1; // <- legal
  ...
  // <- x is defined up to here
}

x = x - 1; // <- illegal, providing there's no other "x" declared

In your case, cust_num is restricted by while {...}. It has to think what value should your code return if cust_num_valid = true and there's no cust_num at all.

  while (!cust_num_valid)
    { // <- Scope of cust_num begins
        cust_num_valid = true;
        Console.Write("Please enter customer number: ");
        string cust_num = Console.ReadLine();

        if (cust_num == "000000" || !Regex.IsMatch(cust_num, @"^[0-9]+$") || cust_num.Length != 6)
        {
            cust_num_valid = false;
            Console.WriteLine("Invalid customer number detected. Customer numbers must be a 6 digit positive integer (zeros will not work)");
        }
    } // <- Scope of cust_num ends

  return cust_num; // <- out of scope

To repair your code put string cust_num = ""; outside the while:

  string cust_num = ""; // <- declaration

  while (!cust_num_valid)
    { 
        cust_num_valid = true;
        Console.Write("Please enter customer number: ");
        cust_num = Console.ReadLine(); // <- no new declaration: "string" is removed

        if (cust_num == "000000" || !Regex.IsMatch(cust_num, @"^[0-9]+$") || cust_num.Length != 6)
        {
            cust_num_valid = false;
            Console.WriteLine("Invalid customer number detected. Customer numbers must be a 6 digit positive integer (zeros will not work)");
        }
    } 

  return cust_num; 

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