ÓÔÁÒ ÔÒÅË ÄÁÔÁ ÂÁÓÅ

BY ÌEN ÌINDSAY

É WANTED TO WRITE A PROGRAM TO
DEMONSTRATE FILE HANDLING, ESPECIALLY
WITH RANDOM FILES. ÓTAR ÔREK
PRESENTED ITSELF AS AN EXCELLENT
TOPIC. ÔHIS SCIENCE FICTION SHOW HAS
BEEN ON THE AIR FOR 20 YEARS NOW,
WITH A TOTAL OF 79 EPISODES. É
CREATED A DATA BASE SYSTEM THAT CAN
EASILY KEEP TRACK OF ALL OF THESE
SHOWS. ÖERY LITTLE IN THIS DATA BASE
IS SPECIFIC TO ÓTAR ÔREK.

É 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. ÔHE TITLES FOR EACH OF
THE 8 MAIN FIELDS CAN VARY DEPENDING
ON WHAT INFORMATION YOU WISH TO KEEP
TRACK OF. ÆOR MY ÓTAR ÔREK SHOWS É
CHOSE THE FOLLOWING:

ÓHOW ÎAME :
×RITER    :
ÁIR ÄATE  :
ÇUEST ÓTAR:
          :
ÃHARACTERS:
          :
ÌOCATION  :

É'VE ALSO PROVIDED TWO EXTRA "USER"
FIELDS. ÔHE FIRST IS AN "ÓTAR ÄATE"
OF 6 CHARACTERS. ÃURRENTLY THE STAR
DATE THAT IS MENTIONED (IF ANY) IS
ENTERED, BUT 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. ÔHE
OTHER FIELD IS ONLY ONE CHARACTER. ÉT
CAN BE USED TO RATE EACH SHOW (Á,Â,Ã,
ETC). É USE IT TO MARK THE SHOWS THAT
É HAVE SEEN. ÉF MARKED, THE ENTIRE
SHOW IS SHOWN IN REVERSE (WHITE ON
BLACK).

ÃHARLES ÐHILLIPS WAS NICE ENOUGH TO
TYPE IN ALL 79 EPISODES. ÏNCE YOU
HAVE A DATA BASE FILLED WITH
INFORMATION, IT IS EASY AND FUN TO
USE.

ÆOR EXAMPLE, LET'S SAY YOUR FAVORITE
AUTHOR IS ÈARLEN ÅLLISON. ÕSING THE
DATA BASE SYSTEM, YOU CAN CHOOSE THE
ÓEARCH OPTION, AND IT WILL LIST EVERY
SHOW WRITTEN BY HIM. ÔHE NICE THING
ABOUT THIS IS THAT THE SYSTEM USES
ÃÏÍÁÌ'S ÉÎ OPERATOR TO FIND THE
MATCHES. ÔHUS, YOU CAN ASK THE SYSTEM
TO LOOK FOR "AR" AND IT WILL FIND
BOTH ÈARLEN ÅLLISON AND ÄAVID
ÇARROLD. ÒEMEMBER, THE SEARCH IS VERY
PICKY ON UPPER OR LOWER CASE. ÔHUS,
ÃYB WILL NOT MATCH ÃÙÂ.

ÓINCE THIS SYSTEM USES A RANDOM FILE
FOR ITS DATA, IT IS EASY TO RANDOMLY
DISPLAY ANY SHOW. ÊUST TYPE IN THE
SHOW NUMBER, AND INSTANTLY (ALMOST)
ITS INFORMATION IS DISPLAYED. ÔO SEE
THE NEXT SHOW JUST TYPE + (PLUS
SIGN). ÔO SEE THE PREVIOUS SHOW TYPE
- (MINUS SIGN).

ÁNOTHER NICE FEATURE OF THIS SYSTEM
IS ÂÒÏ×ÓÅ. ÉT ALLOWS YOU TO SCAN OVER
ALL THE ENTRIES, ONE AFTER ANOTHER,
STARTING AFTER THE SHOW CURRENTLY
DISPLAYED. ÉT EVEN HAS A VARIABLE
PAUSE BETWEEN SHOWS. ÆIVE SECONDS IS
THE DEFAULT, BUT FOR A FAST SCAN, USE
0 FOR THE LENGTH OF PAUSE.

ÎÏÔÅÓ ÁÂÏÕÔ ÔÈÅ ÐÒÏÇÒÁÍ

ÔHE VARIABLE MARK$ IS USED TO
DETERMINE WHETHER OR NOT THE
INFORMATION DISPLAY IS NORMAL OR
REVERSE FIELD. ÔHE SEVENTH LINE OF
THE PROGRAM IS:

DISPLAY(MARK$<> " ")

ÄISPLAY IS THE NAME OF THE PROCEDURE
THAT PRINTS THE INFORMATION ABOUT THE
SHOW TO THE SCREEN. ÉT HAS ONE
NUMERIC PARAMETER. ÉF THE PARAMETER
IS ÆÁÌÓÅ (A VALUE OF 0) THEN THE
INFORMATION IS DISPLAYED NORMALLY. ÉF
IT IS ÔÒÕÅ (A VALUE NOT EQUAL TO 0)
THEN THE INFORMATION IS DISPLAYED IN
REVERSE FIELD. ÍARK$<> " " IS A
COMPARISON THAT WILL ALWAYS BE EITHER
ÔÒÕÅ OR ÆÁÌÓÅ, THUS PROVIDING THE
PROPER PARAMETER.

ÎOTICE THAT TO HAVE THE REVERSE
DISPLAY, EACH VALUE PRINTED MUST BE
THE CORRECT LENGTH BECAUSE THE
REVERSE FIELD WILL STOP AT THE LAST
CHARACTER. ÔHE LENGTH USED IN THIS
PROGRAM IS 27. ÔHUS, IF THE SHOW NAME
IS LESS THAN 27 CHARACTERS, É HAD TO
DO SOMETHING TO PRINT REVERSE FIELD
SPACES AT THE END OF THE NAME. É LET
ÃÏÍÁÌ TAKE CARE OF THIS FOR ME BY
USING SUBSTRING NOTATION WHEN
INPUTING THIS DATA (FROM BOTH
KEYBOARD INPUT AND FILE INPUT). ÆOR
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$)

ÒUN THAT PROGRAM AND TYPE ÔÅÓÔ AS THE
NAME BOTH TIMES IT ASKS. ÔHE FIRST
TIME IT HAS A LENGTH OF 4. ÔHE LAST
TIME IT HAS A LENGTH OF 27 (THE VALUE
WAS PADDED WITH SPACES AT THE END).
ÐRINTING IT EACH TIME IN REVERSE
FIELD SHOWS HOW THE (1:27) TAKES CARE
OF FORMATTING PROBLEMS FOR ME!

ÃALCULATING THE CORRECT RECORD LENGTH
IS ALSO IMPORTANT WHEN USING RANDOM
FILES. ÕSE THE MAXIMUM POSSIBLE
LENGTH AS THE LENGTH FOR THE FILE. ÉN
THIS CASE É HAD 8 FIELDS OF 27
CHARACTERS, 1 FIELD OF 11 CHARACTERS,
AND 1 FIELD OF 1 CHARACTER. ÓINCE
EACH FIELD IS A STRING, É ALSO MUST
ADD A 2 BYTE COUNTER FOR EACH FIELD.
ÔHUS 8*29 PLUS 13 PLUS 3 GIVES 248.
ÔHE SMALLEST RECORD SIZE É CAN USE
AND BE SURE TO HOLD ALL POSSIBLE DATA
IS 248, WHICH É SET IN THE START'UP
PROCEDURE.

ÔO CALCULATE RECORD LENGTH WHEN USING
×ÒÉÔÅ ÆÉÌÅ REMEMBER THESE RULES:

* Á REAL NUMBER ALWAYS NEEDS 5 BYTES
* ÁN INTEGER NEEDS 2 BYTES IN ÃÏÍÁÌ
2.0
  ÁN INTEGER NEEDS 5 BYTES IN ÃÏÍÁÌ
0.14
* Á STRING NEEDS ITS MAXIMUM LENGTH
  ÐÌÕÓ 2 BYTES FOR A LENGTH COUNTER

ËNOWING HOW MANY RECORDS HAVE BEEN
WRITTEN IS ALSO IMPORTANT WHEN USING
RANDOM FILES. ÉF YOU ATTEMPT TO READ
A RECORD PAST THE LAST EXISTING ONE,
AN ERROR OCCURS! Á COMMON WAY TO KEEP
TRACK OF THE LAST RECORD NUMBER IS TO
×ÒÉÔÅ IT INTO THE FIRST RECORD OF THE
FILE:

WRITE FILE 2,1: LAST'RECORD

ÌAST'RECORD IS A VARIABLE THAT HOLDS
THE NUMBER OF THE LAST RECORD WRITTEN
TO THE FILE. ÎOW, 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

ÔHE ONLY SIDE EFFECT OF THIS IS THAT
YOU CANNOT USE THE FIRST RECORD FOR
REGULAR DATA. ÏFTEN, THIS IS NOT A
PROBLEM. ÆOR EXAMPLE, IN OUR ORDER
PROCESSING SYSTEM PROGRAMS (RUNNING
UNDER ÉÂÍ ÐÃ ÃÏÍÁÌ) ÃÏÍÁÌ ÔODAY
SUBSCRIBERS ARE PART OF A RANDOM
FILE, STORED BY THEIR SUBSCRIBER
NUMBER. ÓINCE É USE THE FIRST RECORD
TO HOLD THE LAST SUBSCRIBER'S NUMBER,
É STARTED MY SUBSCRIBER COUNT WITH 2.
ÔHUS THERE IS NO SUBSCRIBER NUMBER 1.

ÂUT IN KEEPING TRACK OF ÓTAR ÔREK
SHOWS, THERE IS A SHOW NUMBER 1.
ÓINCE 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). ÔHUS SHOW NUMBER 1 IS STORED
IN RECORD NUMBER 2. ÂOTH READ'RECORD
AND WRITE'RECORD PROCEDURES DO THE
RECORD NUMBER CONVERSION.

ÁNOTHER THING É TRY TO DO IS KEEP MY
FILES CLOSED AS MUCH AS POSSIBLE. ÏN
A ÃOMMODORE DISK, ALL FILES MUST BE
PROPERLY CLOSED OR THEY CAN'T BE
OPENED LATER. ÓO, É TAKE PRECAUTIONS
(IN CASE OF A POWER OUTAGE ETC.) AND
KEEP THE FILE CLOSED WHEN IT IS NOT
DIRECTLY BEING USED. ÆOR EXAMPLE,
WHILE SEARCHING THE FILE FOR MATCHES,
É USE THE PROCEDURE READ'RECORD
DIRECTLY, AND DON'T CLOSE THE FILE
AFTER EACH RECORD IS READ. É ONLY
CLOSE THE FILE AFTER É FIND A MATCH.
ÈOWEVER, WHEN JUST GETTING
INFORMATION ABOUT ONE SHOW, É HAVE
THE PROCEDURE READ'IT WHICH FIRST
OPENS THE FILE, THEN READS THE
RECORD, THEN CLOSES THE FILE. ÔHUS
THE FILE IS CLOSED WHILE É LOOK AT
THAT RECORD (AND POSSIBLY EDIT IT).
ÎOTE THAT É ALWAYS CLOSE THE FILE
AFTER É WRITE TO IT. ÔHUS É ONLY HAVE
ONE WRITE'RECORD PROCEDURE.

ÒEMEMBER, THE DATA IS ONE OF THE MOST
IMPORTANT PARTS OF THIS DATA BASE
SYSTEM! ÔHE DATA IS IN THE FILE
"RAN.STARTREK".