Is this a good use of goto statement?

Question

I am writing a simple C# console application in which I am solving the problem by using a GoTo statment to return to the label if the input for UserId is not valid.

But I am not sure if I am using the statement correctly. I would like to work around if there is a better way to solve the problem, even without using GoTo statement?

public void CreateAccount()
{
    Console.WriteLine("----- Create New Account -----\n" +
        "Enter following account information:\n");

    getUserID:
    {
        Console.WriteLine("Enter a UserID (Alphanumeric; no special characters): ");
        string userid = Console.ReadLine();
        if (!ValidUserID(userid))
        {
            Console.WriteLine("Userid can only contain A-Z, a-z & 0-9. Try again");
            goto getUserID;
        }
        if (data.IsUserInFile(userid))
        {
            Console.WriteLine("Userid already exists. Try again");
            goto getUserID;
        }
    }
}

I will be using the same approach for other fields such as Pin, AccountType, Balance, AccountStatus etc. so I want to ensure that I am doing this in the right manner before I expand its use.

Answer 1

A simple approach would be to use an if/else if/else construct:

public void CreateAccount()
{
    Console.WriteLine("----- Create New Account -----\n" +
        "Enter following account information:\n");

    string userid = null;
    while (true)
    {
        Console.WriteLine("Enter a UserID (Alphanumeric; no special characters): ");
        userid = Console.ReadLine();
        if (!ValidUserID(userid))
        {
            Console.WriteLine("Userid can only contain A-Z, a-z & 0-9. Try again");
        }
        // if the condition above isn't matched, we'll check this condition
        else if (data.IsUserInFile(userid))
        {
            Console.WriteLine("Userid already exists. Try again");
        }
        // if that isn't matched either, then we have an acceptable userid and can exit the loop
        else
        {
            break;
        }
    }
}

Note that I've moved the userid declaration out of the loop, since you presumably need to use it after the loop.

Alternatively, you could potentially break up your code a little more. The whole method for reading the userId could be moved out into its own method:

public string ReadUserId()
{
    while(true)
    {
        // Prompt and read answer
        Console.WriteLine("Enter a UserID (Alphanumeric; no special characters): ");
        string userId = Console.ReadLine();
        
        // If the id is valid, return it and leave the method (ending the loop)
        if (ValidUserId(userId))
        {
            return userId;
        }
        
        // If we got here, then the id is invalid and we should inform the user to try again
        Console.WriteLine("Userid can only contain A-Z, a-z & 0-9. Try again");
    }
}

Now in the main method we can reference this method when we need to obtain a userId. The loop for checking if the user already exists can now be implemented separately to reading the user input, so there are no longer concerns about two different conditions:

public void CreateAccount()
{
    Console.WriteLine("----- Create New Account -----\n" +
        "Enter following account information:\n");

    string userId = null;
    bool isNewUser = false;
    while (!isNewUser)
    {       
        // Use our other method to read the user id
        userId = ReadUserId();
    
        if (data.IsUserInFile(userId))
        {
            Console.WriteLine("Userid already exists. Try again");
            continue;
        }
        
        isNewUser = true;
    }
}