C# How do I make a switch ignore invalid input?

Question

I am trying to make a simple console game that starts with a title screen. The user inputs 'N' for a new game, 'L' to load a game, or 'E' to exit. I have this set up as a switch, but I need to know how to make the program ignore any input other than the aforementioned keys. I've Googled this question but didn't find an answer. Please help if you can.

I don't see much point in posting the code as 10 lines of a simple switch probably wouldn't be terribly helpful to solving the problem. Also, if there would be an easier / more efficient way than a switch, I would love to know.

Thanks.

Answer 1

You can use a default: statement to handle the other (unknown) cases:

switch(inputString.ToLower())
{
     case "n":
       // Handle new
       break;
     //.. handle known cases
     default:
         Console.WriteLine("Unknown option chosen.  Please enter valid option:");
         // Re-read values, etc?
         break;
}

Anything not specified in one of your other cases will fall into the default case, which you can then use to prompt for valid input.

Answer 2

If you want to actually ignore all keys other than valid ones you could do something like this:

public static char ReadKey(IEnumerable<char> validKeys)
{
    var validKeySet = new HashSet<char>(validKeys);
    while (true)
    {
        var key = Console.ReadKey(true);
        if (validKeySet.Contains(key.KeyChar))
        {
            //you could print it out if you wanted.
            //Console.Write(key.KeyChar);
            return key.KeyChar;
        }
        else
        {
            //you could print an error message here if you wanted.
        }
    }
}

When you use ReadKey(true) the true indicated that it will intercept that key and not display it on the console. This gives you the option of determining if it's valid or invalid.

Answer 3

如果switch语句没有default块，并且如果打开的表达式不匹配任何case块，则switch语句不执行任何操作。

Answer 4

When you have only 3 cases, a switch isn't much more efficient than just a simple if-else construct.

if (input == "N")
{
    // New game
}
else if (input == "L")
{
    // Load game
}
else if (input == "E")
{
    // Exit game
}
// if none of the cases match, the input is effectively ignored.

If you insist on using a switch, then your construct is very similar:

switch (input)
{
    case "N":
        //New Game
        break;
    case "L":
        //Load Game
        break;
    case "E":
        //Exit Game
        break;
    default:
        //Do nothing (ignore unmatched inputs)
        break;
}

Answer 5

Thanks for the replies, guys. I managed to solve the problem by doing the following:

static void titleInput()
    {
        ConsoleKeyInfo titleOption = Console.ReadKey(true);

        switch (titleOption.Key)
        {
            case ConsoleKey.N:
                Console.Clear();
                break;
            case ConsoleKey.L:
                break;
            case ConsoleKey.E:
                Environment.Exit(0);
                break;
            default:
                titleInput();
                break;

        }
    }

I'm not sure how 'proper' this is, but it does what I need it to do. Any keys other than 'N', 'L', and 'E' no longer do anything.