Base converter with fractions?

[Han]

Purposely avoided using the CAS directly so that I could use a "random" variable, resulting in code that does not read well.

EDIT: fixed some bugs

Code:

EXPORT basecalc()
BEGIN
  local maxdigits:=20; // maximum number of digits for frac part

  local j,k,t,run:=1;
  local b1:=10;
  local b2:=16;
  local d:=0;
  local n:="";
  local ds:="";
  local r:=string(rand,1,12); // create a random CAS variable
  local var:="";
  local ipn:=""; // integer part of n
  local fpn:=""; // frac part of n
  
  local digits:="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

  k:=size(r)-2;
  var:="tmp" + right(r,k);


  while run do
    t:=input(
      { 
        { n, [2], { 15, 80, 0 } },
        { b1, [0], { 25, 25, 1 } },
        { b2, [0], { 70, 25, 1 } },
        { maxdigits, [0], {25,25, 2 } }
      },
      "Base Converter",
      { "n=", "base1=", "base2=", "digits=" },
      {
        "Enter the integer",
        "Enter the base of the integer n",
        "Enter the base to convert to",
        "Max allowable digits"
      }
    );

    if t then
      r:=var + ":={0,0}";
      CAS(EVAL(r));
      k:=size(n);
      if (k AND (b1 >= 2) AND (b2 <= 62)) then

        j:=instring(n,".");

        if j then
          if (j-1>0) then ipn:=left(n,j-1); end;
          if (k-j>0) then fpn:=right(n,k-j); end;
          k:=j-2;
        else
          ipn:=n;
          k:=size(n)-1;
        end;

        // k = largest exponent
        t:=size(ipn);
        for j from 1 to t do
          ds:=mid(ipn,j,1);
          d:=instring(digits,ds)-1;
          if ((d >= b1) OR (d < 0)) then msgbox("Invalid digit: " + ds); j:=-1; break; end;
          r:=var + "[1]:=" + var + "[1]+" + d + "*" + b1 + "^" + k;
          k:=k-1;
          CAS(EVAL(r));
        end;
        if (j == -1) then continue; end;

        t:=size(fpn);
        for j from 1 to t do
          ds:=mid(fpn,j,1);
          d:=instring(digits,ds)-1;
          if ((d >= b1) OR (d < 0)) then msgbox("Invalid digit: " + ds); j:=-1; break; end;
          r:=var + "[2]:=" + var + "[2]+" + d + "*" + b1 + "^" + k;
          k:=k-1;
          CAS(EVAL(r));
        end;
        if (j == -1) then continue; end;

        n:="";

        t:=size(ipn);
        if t then
          r:="ip(ln(" + var + "[1])/ln(" + b2 + ")))";
          k:=CAS(EVAL(r));
          for j from k downto 0 do
            r:="ip(" + var + "[1]/(" + b2 + "^" + j + "))";
            d:=CAS(EVAL(r));
            ds:=mid(digits,d+1,1);
            n:=n+ds;
            r:=var + "[1]:=" + var + "[1] - " + d + "*" + b2 + "^" + j;
            CAS(EVAL(r));
          end;
        end;

        t:=size(fpn);
        if t then
          n:=n+".";
          r:="numer(" + var + "[2])"; t:=CAS(EVAL(r));
          r:="denom(" + var + "[2])"; k:=CAS(EVAL(r));
          for j from 1 to maxdigits do
            r:="ip(" + var + "[2]*" + b2 + ")";
            d:=CAS(EVAL(r));
            r:=var + "[2]:=" + var + "[2]*" + b2 + "-" + d;
            CAS(EVAL(r));

            // floating point issue
            r:=var + "[2] < 0";
            if CAS(EVAL(r)) then
              r:=var + "[2]:=" + var + "[2]+1";
              CAS(EVAL(r));
              d:=d-1;
            end;
            ds:=mid(digits,d+1,1);
            n:=n+ds;
            r:=var + "[2] == 0";
            if CAS(EVAL(r)) then break; end;
          end;
        end;

        t:=b1;
        b1:=b2;
        b2:=t;

      else
        msgbox("Invalid input");
      end;

    else
      run:=0;
    end;

  end;

  r:="purge(" + var + ")";
  CAS(EVAL(r));
  return(0);
END;

I'm sure there is another method using numer() and denom() rather than ip().

Basically, enter your integer as n, along with the presumed base1. The program converts n written in base1 into base2 representation, and sets up the program to re-run it in the opposite direction. Hit CANCEL or press ON to stop.