Transformation from one position scale of notation to another

Question

How can I transform from one scale of notation to another using my custom function by C#.

abstract string Convert(string value, string fromBase, string toBase);

value - string representation scale of notation in basic notation

fromBase - string represent the base of numeric

toBase - string representation the base of numeric which you must to transform

P.S. string which represents the base position scale of notation can include any symbols for represent numeral ascending order

For example

Value = “GSAK”

   fromBase = “A,S,G,K” – four(4) is the base scale of notation (If write arabic figures:  0,1,2,3)
   toBase= “0,1,2,3,4,5,6,7,8,9” – ten(10) is the base scale of notation
   return value = “147”

Answer 1

I would first translate the input value to one of the numeric data types (i.e. long), and then encode into the target format. Draft implementation of a class to do the parsing and encoding (untested and certainly not optimal):

public class Formatter
{
  List<char> symbols;
  int base;

  public Formatter(string format)
  {
    string[] splitted = format.Split(",");
    symbols = splitted.Select(x => x[0]).ToList();
    base = symbols.Size;
  }

  public long Parse(string value)
  {
    long result = 0;
    foreach(char c in value)
    {
      long n = symbols.IndexOf(c);
      result = result*base+n;
    }
    return result;
  }

  public string Encode(long value)
  {
    StringBuilder sb = new StringBuilder();
    while(value>0)
    {
      long n = value % base;
      value /= base;
      sb.Insert(0, symbols[n]);
    }
    return sb.ToString();
  }
}