using System;

using System.Text;

public class Program

{

    public static void Main()

    {

        for(long value=0; value < 100; value++)

        {

            Test(value, "01");

            Console.Write("\t");

            Test(value, "AB");

            Console.Write("\t");

            Test(value, 10);

            Console.Write("\t");

            Test(value, 16);

            Console.Write("\t");

            Test(value, 10 + 26 + 26);

            Console.Write(Environment.NewLine);

        }

    }

    public static void Test(long value, int targetBase, int padding = 8)

    {

        var converter = new BaseConverter(value, targetBase);

        var result = converter.ToString(padding);

        Console.Write("value={0} to base{1} => {2}", value, targetBase, result);

    }

    public static void Test(long value, string source, int padding = 8)

    {

        var converter = new BaseConverter(value, source);

        var result = converter.ToString(padding);

        Console.Write("value={0} to base{1} => {2}", value, source, result);

    }

}

​

public class BaseConverter

{

    public static readonly string Source_Numeric = "0123456789";

    public static readonly string Source_LowerCase = "abcdefghijklmnopqrstuvwxyz";

    public static readonly string Source_UpperCase = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    public static readonly string Source_FullRange;

​

    private string _source;

    static BaseConverter()

    {

        Source_FullRange = string.Concat(Source_Numeric, Source_UpperCase, Source_LowerCase);

    }

    public BaseConverter(long value)

            : this(value, Source_FullRange)

    {

    }

    public BaseConverter(long value, int targetBase)

        : this(value, Source_FullRange.Substring(0, targetBase))

        {

            if (targetBase > _source.Length)

                throw new ArgumentOutOfRangeException("base can't be greater than " + _source.Length);

        }

    public BaseConverter(long value, string source)

    {

        if (source.Length <= 1)

            throw new ArgumentOutOfRangeException("base must be at greater than 1");

        if (source.Length > Byte.MaxValue)

            throw new ArgumentOutOfRangeException("base can't be longer than " + Byte.MaxValue);

        Value = value;

        _source = source;

    }

    public long Value { get; private set; }

    public byte Base { get { return (byte)_source.Length; } }

    public override string ToString()

    {

        return ToStringInternal();

    }

    public string ToString(int paddingLen)

    {

        var pad = _source[0];

        var result = ToStringInternal();

        return result.PadLeft(paddingLen, pad);

    }

    private string ToStringInternal()

    {

        var value = Value;

        var targetBase = (byte)_source.Length;

        var sb = new StringBuilder();

        do

        {

            var index = (int)(value % targetBase);

            sb.Insert(0, _source[index]);

            value /= targetBase;

        } while(value > 0);

        return sb.ToString();

    }

}

​