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

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);
}