Ahoy 1987 July/Ahoy_Magazine_87-07_1987_Double_L_Side_B.d64/doctor who.txt

Text File | 2022-10-26 | 7KB | 243 lines

Doctor Who Data Base

by Len Lindsay

This disk I wanted to have several
programs demonstrate file handling,
especially with random files. Doctor
Who presented itself as an excellent
topic. This science fiction show has
been on the air for 24 years now,
with a total of over 150 movie length
shows. In each show, the Doctor has
varying companions, and meets
different adversaries (and even
interesting monsters). So, I created
a data base system that can easily
keep track of a series of shows. Very
little in this data base is specific
to Doctor Who (to illustrate this, we
also are including Star Trek data on
the disk). I used 8 fields of 27
characters each to store the data for
a show, plus two extra fields that
you can decide how to use. The titles
for each of the 8 main fields can
vary depending on what information
you wish to keep track of. For the
Doctor Who shows I chose the
following:

Show Name:
Doctor:
Companion1:
Companion2:
Companion3:
Adversary1:
Adversary2:
Location:

I've also provided two extra "user"
fields. The first is an "ID" of 11
characters. You could put the video
tape number here, the name of your
friend who has this show on tape, or
a short comment on the show. The
other field is only one character. It
can be used to rate each show (A,B,C,
etc). I use it to mark the shows that
I have seen.

Since I am a true Doctor Who fan, I
have painstakenly entered all the
data for the first 144 shows! This
large data base of information is on
this disk along with the data base
program itself. Once you have a data
base filled with information, it is
easy and fun to use.

For example, let's say your favorite
Doctor Who adversaries were the
CYBERMEN. Using the data base system,
you can choose the Search option, and
it will list every show that included
cybermen as adversaries! The nice
thing about this is that the system
uses COMAL's IN operator to find the
matches. Thus, you can ask the system
to look for CYB and it will find both
CYBERMEN as well as their "pets", the
CYBERMATS. Remember, the search is
very picky on upper or lower case.
Thus, Cyb will not match CYB.
Therefore, you may wish to do as I
did on my data -- never use shifted
letters! (Or always capitalize the
first letter of each word).

Since this system uses a random file
for its data, it is easy to randomly
display any show. Just type in the
show number, and instantly (almost)
its information is displayed. To see
the next show just type + (plus
sign). To see the previous show type
- (minus sign).

Another nice feature of this system
is BROWSE. It allows you to scan over
all the entries, one after another,
starting after the show currently
displayed. It even has a variable
pause between shows. Five seconds is
the default, but for a fast scan, use
0 for the length of pause.

NOTES ABOUT THE PROGRAM

The variable mark$ is used to
determine whether or not the
information display is normal or
reverse field. Near the beginning of
the program you will see this
statement:

display(mark$<> " ")

DISPLAY is the name of the procedure
that prints the information about the
show to the screen. It has one
numeric parameter. If the parameter
is FALSE (a value of 0) then the
information is displayed normally. If
it is TRUE (a value not equal to 0)
then the information is displayed in
reverse field. Mark$<> " " is a
comparison that will always be either
TRUE or FALSE, thus providing the
proper parameter.

Notice that to have the reverse
display, each value printed must be
the correct length because the
reverse field will stop at the last
character. The length used in this
program is 27. Thus, if the show name
is less than 27 characters, I had to
do something to print reverse field
spaces at the end of the name. I let
COMAL take care of this for me by
using substring notation when
inputing this data (from both
keyboard input and file input). For
example:

dim name$ of 27
input "name:": name$
print chr$(18)+name$
print "length is";len(name$)
input "name:": name$(1:27)
print chr$(18)+name$
print "length is";len(name$)

Run that program and type TEST as the
name both times it asks. The first
time it has a length of 4. The last
time it has a length of 27 (the value
was padded with spaces at the end).
Printing it each time in reverse
field shows how the (1:27) takes care
of formatting problems for me!

Calculating the correct record length
is also important when using random
files. Use the maximum possible
length as the length for the file. In
this case I had 8 fields of 27
characters, 1 field of 11 characters,
and 1 field of 1 character. Since
each field is a string, I also must
add a 2 byte counter for each field.
Thus 8*29 plus 13 plus 3 gives 248.
The smallest record size I can use
and be sure to hold all possible data
is 248, which I set in the start'up
procedure.

To calculate record length when using
WRITE FILE remember these rules:

* A real or integer number uses 5
bytes
* A string needs its maximum length
PLUS 2 bytes for a length counter

Knowing how many records have been
written is also important when using
random files. If you attempt to read
a record past the last existing one,
an error occurs! A common way to keep
track of the last record number is to
WRITE it into the first record of the
file:

write file 2,1: last'record

Last'record is a variable that holds
the number of the last record written
to the file. Now, each time you use
that file, you can simply read the
last record number from the file like
this:

read file 2,1: last'record

The only side effect of this is that
you cannot use the first record for
regular data. Often, this is not a
problem. For example, in our order
processing system programs (running
under IBM PC COMAL) COMAL Today
subscribers are part of a random
file, stored by their subscriber
number. Since I use the first record
to hold the last subscriber's number,
I started my subscriber count with 2.
Thus there is no subscriber number 1.

But in keeping track of Doctor Who
shows, there is a show number 1.
Since it can't be written into record
number 1, we simply add 1 to the show
number to give the record number
(read this sentence twice - it makes
sense). Thus show number 1 is stored
in record number 2. Both read'record
and write'record procedures do the
record number conversion.

Another thing I try to do is keep my
files closed as much as possible. On
a Commodore disk, all files must be
properly closed or they can't be
opened later. So, I take precautions
(in case of a power outage etc.) and
keep the file closed when it is not
directly being used. For example,
while searching the file for matches,
I use the procedure read'record
directly, and don't close the file
after each record is read. I only
close the file after I find a match.
However, when just getting
information about one show, I have
the procedure read'it which first
opens the file, then reads the
record, then closes the file. Thus
the file is closed while I look at
that record (and possibly edit it).
Note that I always close the file
after I write to it. Thus I only have
one write'record procedure.