Question

I am using the following class method to create a Base36 string from a number:

private const string CharList = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

public static String Encode(long input) {
    if (input < 0) throw new ArgumentOutOfRangeException("input", input, "input cannot be negative");
        char[] clistarr = CharList.ToCharArray();
        var result = new Stack<char>();
        while (input != 0)
        {
            result.Push(clistarr[input % 36]);
            input /= 36;
        }
        return new string(result.ToArray());
    }

One of the requirements is that the string should always be padded with zero’s and should be a maximum of four digits. Can anyone suggest a way that I can code the leading zero’s and also limit the function so it will never return more than “ZZZZ” ? Is there some function in C# that can do this. Sorry about the indentation on this code. I am not sure why it’s not indenting properly.

Answer 1

If there are always going to be exactly four digits, it’s really easy:

const long MaxBase36Value = (36L * 36L * 36L * 36L) - 1L;

public static string EncodeBase36(long input)
{
    if (input < 0L || input > MaxBase36Value)
    {
        throw new ArgumentOutOfRangeException();
    }
    char[] chars = new char[4];
    chars[3] = CharList[(int) (input % 36)];
    chars[2] = CharList[(int) ((input / 36) % 36)];
    chars[1] = CharList[(int) ((input / (36 * 36)) % 36)];
    chars[0] = CharList[(int) ((input / (36 * 36 * 36)) % 36)];
    return new string(chars);
}

Or using a loop:

const long MaxBase36Value = (36L * 36L * 36L * 36L) - 1L;

public static string EncodeBase36(long input)
{
    if (input < 0L || input > MaxBase36Value)
    {
        throw new ArgumentOutOfRangeException();
    }
    char[] chars = new char[4];
    for (int i = 3; i >= 0; i--)
    {
        chars[i] = CharList[(int) (input % 36)];
        input = input / 36;            
    }
    return new string(chars);
}