'**********************************************
'* This program converts a number in base a   *
'* into a number in base b (a and b must be   *
'* between 2 and 36).                         *
'* ------------------------------------------ *
'* Ref.: "Mathematiques en Turbo-Pascal by    *
'*        M. Ducamp and A. Reverchon (2),     *
'*        Eyrolles, Paris, 1988" [BIBLI 05].  *
'* ------------------------------------------ *
'* Sample runs:                               *
'*                                            *
'* BASE CONVERSION                            *
'*                                            *
'* Start  base (2 to 36): 5                   *
'* Arival base (2 to 36): 3                   *
'*                                            *
'* Enter number in start base: 3421           *
'* In base 3: 200000                          *
'* Enter number in start base: 3420           *
'* In base 3: 122222                          *
'*                                            *
'*                                            *
'* BASE CONVERSION                            *
'*                                            *
'* Start  base (2 to 36): 10                  *
'* Arival base (2 to 36): 16                  *
'*                                            *
'* Enter number in start base: 65535          *
'* In base 3: FFFF                            *
'* Enter number in start base: 100            *
'* In base 3: 64                              *
'*                                            *
'* BASE CONVERSION                            *
'*                                            *
'* Start  base (2 to 36): 16                  *
'* Arival base (2 to 36): 2                   *
'*                                            *
'* Enter number in start base: FF             *
'* In base 3: 11111111                        *
'* Enter number in start base: 3A             *
'* In base 3: 111010                          *
'* Enter number in start base: E2             *
'* In base 3: 11100010                        *
'*                                            *
'* Note: Enter null string to exit.           *
'*                                            *
'*                Basic Release by J-P Moreau *
'*                      (www.jpmoreau.fr)     *
'**********************************************
'Explanations:
'------------
'The letters A,B,...,Z  represent 10,11,...,36
'in the base > 10.

'The number is first converted from base a to
'base 10 by Function Decodebase, then  converted
'from base 10 to base b by Function Codebase.
'-----------------------------------------------
defint i-n

XMAXREAL = 1E30

'  iba,ibd: INTEGER
'  x$,y$: STRING
'  r: REAL

'main program
  cls
  print
  print " BASE CONVERSION"
  print
  input " Start  base (2 to 36): ", ibd
  input " Arival base (2 to 36): ", iba
10 print
  input " Enter number in start base: ", x$
    if x$<>"" then
      gosub 1000  'Decodebase(x$,ibd,r)
      if IERROR=0 then
        gosub 2000  'Codebase(r,iba,y$)
        if IERROR=0 then
          print " In base "; iba; ": "; y$
        else
          print " Error in coding number."
        end if
      else
        print " Errorin decoding number."
      end if
    end if
  if x$<>"" then goto 10
  print
END

'Convert a number x$ from base ibd to base 10. The subroutine set
'IERROR to 1 if ibd not in [2..36] or if string x$ contains invalid
'characters in base ibd or if result r is too big, else IERROR=0.
'Subroutine Decodebase(x$,ibd,r)
'xmult: REAL
'ch$:CHAR
1000  IERROR=1
  if ibd<2 or ibd>36 then
    print " base must be between 2 and 36 !"
    return
  end if
  r=0 : xmult=1
  long=len(x$)
  for i=1 to long
    ch$=mid$(x$,long+1-i,1)
    if ch$<"0" or ch$>"Z" or (ch$>"9" and ch$<"A") then return
    if ch$<="9" then
      j=asc(ch$)-asc("0")
    else
      j=asc(ch$)-asc("A")+10
    end if
    if j>=ibd then return
    r=r+xmult*j
    if xmult>XMAXREAL/ibd then return
    xmult=xmult*ibd
  next i
  IERROR=0
Return


'Convert a number r from base 10 to base iba. The subroutine set
'IERROR to 1 if iba not in [2..36], else IERROR=0.
'Subroutine Codebase(r,iba,y$)
2000 IERROR=1
  if iba<2 or iba>36 then
    print " base must be between 2 and 36 !"
    return
  end if
  y$="": x=r
2010 if x<=0 then goto 2020
    n=INT(x-iba*INT(x/iba))
    if n<10 then
      y$=Chr$(Asc("0")+n)+y$
    else
      y$=Chr$(Asc("A")+n-10)+y$
    end if
    x=INT(x/iba)
  goto 2010
2020 IERROR=0
Return

'end of file basis.bas