Variable does not exist in the current context?

c#, return, scope

Solution

Each variable in C# 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;

Problem

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; } ```

Original source