Alphanumeric Counter

Question

I am trying to create in C# an alphanumeric counter that creates numbers in the following way:

0001
0002
0003
...
9999
A000
A001
...
A999
B000
...

The last number would be ZZZZ. So it would 0-9 first, then A-Z after that.

I am lost on how this can be done.

Answer 1

Update: After your comment I think there is a mistake in your question. What you probably want is just a simple base 36 counter. Here's one way you could implement it:

string base36Characters = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

string toBase36(int x, int digits)
{
    char[] result = new char[digits];
    for (int i = digits - 1; i >= 0; --i)
    {
        result[i] = base36Characters[x % 36];
        x /= 36;
    }
    return new string(result);
}

IEnumerable<string> base36Counter()
{
    for (int n = 0; n < 36 * 36 * 36 * 36; ++n)
    {
        yield return toBase36(n, 4);
    }
}

void Run()
{
    foreach (string s in base36Counter())
        Console.WriteLine(s);
}

---

Original answer: I would probably implement it using yield:

IEnumerable<string> magicCounter()
{
    // 0000, 0001, ..., 9999
    for (int i = 0; i < 10000; ++i)
    {
        yield return i.ToString("0000");
    }

    // A000, A001, ..., Z999
    for (char c = 'A'; c <= 'Z'; ++c)
    {
        for (int i = 0; i < 1000; ++i)
        {
            yield return c + i.ToString("000");
        }
    }
}

Answer 2

Edit: Updated to answer the clarified question.

The following code will generate the counter you describe:

0000, 0001... 9999, A000... A999, B000... Z999, ZA00... ZA99, ZB00... ZZ99, ZZA0... ZZZ9, ZZZA... ZZZZ

public const int MAX_VALUE = 38885;

public static IEnumerable<string> CustomCounter()
{
    for (int i = 0; i <= MAX_VALUE; ++i)
        yield return Format(i);
}

public static string Format(int i)
{
    if (i < 0)
        throw new Exception("Negative values not supported.");
    if (i > MAX_VALUE)
        throw new Exception("Greater than MAX_VALUE");

    return String.Format("{0}{1}{2}{3}",
                         FormatDigit(CalculateDigit(1000, ref i)),
                         FormatDigit(CalculateDigit(100, ref i)),
                         FormatDigit(CalculateDigit(10, ref i)),
                         FormatDigit(i));
}

private static int CalculateDigit(int m, ref int i)
{
    var r = i / m;
    i = i % m;
    if (r > 35)
    {
        i += (r - 35) * m;
        r = 35;
    }
    return r;
}

private static char FormatDigit(int d)
{
    return (char)(d < 10 ? '0' + d : 'A' + d - 10);
}