GFA PROGRAMMING TIPS
                             ====================

                                By John Charles

    Three tips  for  GFA  Basic3  programmers  using  coding  from  JCLABEL
    originally  written  for  GFA   Basic   Users   Group  Diskzine  (GBUG,
    California, USA) in 1993

    WHERE IS MY PROGRAM ????????

    When the user of your program wants to  load or save a file it is often
    useful to present  the  user  with  the  file-selector  pointing at the
    folder which contains the program. The following two lines of code when
    placed  near  the  beginning   of   the   program   code  (or  in  your
    initialisation procedure) will let you  know  exactly where the program
    was when it was first run....

    drive%=GEMDOS(25)

    disk$=CHR$(drive%+65)+":"+DIR$(0)+"\"

    The first line returns a number in drive%

    where 0 = drive A, 1 = drive B, 2 = drive C, etc.....

    The second line converts  this  to  the correct letter CHR$(drive%+65),
    adds the colon, makes a call DIR$(0) which returns the rest of the path
    and finally adds a final backslash.

    So, if the program JCLABEL is on drive  E and buried in a folder called
    JC_PROGS and then inside  another  folder  called  JCLABEL the variable
    disk$ will contain E:\JC_PROGS\JCLABEL\

    If it was in the root directory of  a floppy in drive A then disk$ will
    just contain A:\

    This information may be used when you call the file-selector to present
    this path when looking for the label lists...

    I then use...

    FILESELECT #"LOAD AN ADDRESS LIST",disk$+"*.JCL",default$,fname$

    to call the file-selector which does several things at once.

    First using the #  variation  lets  you  send  a  message  to the file-
    selector which will be printed at the  top  if you have TOS1.4 or later
    or are using a third  party  file-selector  like UISIII or Little Green
    Selector. In this case the message LOAD AN ADDRESS LIST is sent.

    Next the route to the  folder  containing  the  program is sent (disk$)
    which has, in this case, *.JCL added so the fileselector shows only the
    files ending with the extender JCL

    Thirdly, default$ should contain the name  of any default file-name you
    may want to present to the user otherwise just use a null string ("")

    In my case I use

    default$=disk$+"MYADLIST.JCL"

    Lastly the variable fname$ lets you  know  what the user has chosen. If
    they selected a file or typed in  a  file-name and clicked OK or double
    clicked on a file-name, fname$  will  contain  the full path along with
    the name of the file. If they clicked CANCEL then fname$ will be a null
    string "".

    KEEPING AN AUTOMATIC BACKUP FILE

    Some programs automatically keep a backup  of  the last copy of a file,
    just in case it  is  needed  again.  JCLABEL  now  does  this as it was
    requested by a user with  several  long  address  lists who lost one by
    typing the wrong name late one tiring night.

    How can you do that then? Easily  as  long  as one or two simple checks
    are made along the way.

    Here is part of the code from JCLABEL...

    bakup$=LEFT$(fname$,LEN(fname$)-3)+"BAK"

    IF EXIST(bakup$)

      KILL bakup$

    ENDIF

    IF EXIST(fname$)

      RENAME fname$ AS bakup$

    ENDIF

    That's it!! Next the code carries on to save the new file as normal.

    To explain the above...

    First take the  full  path  and  filename  which  the file-selector has
    returned to you in fname$ (or whatever  you  want to call it) and strip
    off the last three characters which is what LEFT$(fname$,LEN(fname$)-3)
    does and add in the new BAK extension.

    Next check to see if an old backup file already exists and delete it.

    Now see if the original file-name already exists and rename it with the
    extender BAK

    It may seem a strange order  to  do  the things but this process covers
    all eventualities and doesn't  fall  flat  on  its  face  if it's a new
    filename (nothing to backup and no backup  to  delete) or if there is a
    file which hasn't been backed up yet.

    I find that the error  checking  sections  of programming take the most
    thinking out (trying to  imagine  all  possible  actions and mistakes a
    user might make) and the longest testing time but in the end it's these
    little bits which the user never  notices  but which can make a program
    user friendly.

    I hope that these few hints will  have been useful to someone out there
    starting with GFA - don't  give  up  too  easily,  we all have to start
    somewhere and there's always someone willing to answer queries.

    This text file may  be  distributed  freely  by  anyone  for non profit
    purposes as long as it remains unaltered.

    BeST wishes  >> JayCee <<  March, 1994