148 lines
5.3 KiB
Plaintext
148 lines
5.3 KiB
Plaintext
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=======================================
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= HP 2000 PART 4 (FILES) =
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= CAPTURED BY =
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= BLITZIOD ?? & GALACTUS ** =
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= of =
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= THE ELITE HACKERS GUILD =
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=======================================
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* FILES *
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BASIC FORMATTED FILES ARE ESSENTIALLY THE SAME AS
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DATA STATEMENTS, THEY BOTH HAVE POINTERS THAT MOVE ALONG THE DATA
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HERE IS AN EXAMPLE OF A PROGRAM USING THE DATA STATEMENT :
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10 READ X
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20 PRINT X
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30 DATA 1,2,3,4,5,6,7,8,9,10
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40 GOTO 10
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50 END
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WHEN THIS PROGRAM IS RUN THE DATA IS READ IN LINE 10
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FROM THE DATA STATEMENT IN LINE 30.
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AFTER THE '1' IS READ FROM THE DATA STATEMENT THE POINTER IS
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MOVED TO THE '2' AND SO ON. WHEN THE FINAL PIECE OF DATA IS READ
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AND THE POINTER IS MOVED BEYOND THE '10' THEN YOU WILL GET THE
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ERROR MESSAGE: OUT OF DATA IN LINE 10
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THIS IS ESSENTIALLY THE WAY FILES WORK.
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BUT FILES HAVE MANY MORE CAPABILITIES THAN DO DATA STATEMENTS
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LET'S LEARN HOW TO CREATE A FILE, OK?
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TO CREATE A FILE ALL ONE MUST DO IS TYPE IN CRE- THEN THE
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NAME OF THE FILE, AND HOW LONG IT MUST BE. FOR EXAMPLE IF I WANTED
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TO CREATE A FILE NAMED 'DAVID' THAT IS 5 RECORDS LONG I WOULD TYPE IN
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CRE-DAVID,5
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THEN HIT 'RETURN'
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WHENEVER YOU CREATE A FILE THE COMPUTER RESERVES THE NUMBER OF
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RECORDS YOU CREATED IT ON THE DISC. SO IF YOU CREATE A FILE THAT
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IS 50 RECORDS LONG, YOU HAVE USED 50 RECORDS OF DISC SPACE, WHETHER
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YOU USE THE WHOLE FILE OR NOT.
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NOW I WILL SHOW YOU A PROGRAM THAT WILL PRINT ON YOUR FILE.
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5 DIM A$(20), B$(20)
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10 FILES FIL1
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20 PRINT 'NAME';
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30 INPUT A$
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40 IF END#1 THEN 85
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50 READ#1,1
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60 READ#1;B$
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70 GOTO 60
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85 IF END#1 THEN 110
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90 PRINT#1;A$,END
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100 STOP
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110 PRINT'FILE FULL'
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120 END
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BY THIS TIME YOU ARE WONDERING WHAT THAT MESS IS, RIGHT ?
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HERE IS AN EXPLANATION
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STATEMENT # MEANING
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10 OPENS THE FILE THAT IS TO BE USED, IN THIS CASE THE NAME OF
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THE FILE IS 'FIL1'. THIS STATEMENT IS TELLING THE COMPUTER
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WHAT FILE WE WANT TO USE FOR THIS PROGRAM
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FIL1 IS REFERRED TO AS #1 AS SEEN IN LINES 40,50 & 60
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IF MORE THAN ONE FILE WAS USED LINE 10 WOULD LOOK LIKE
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THIS FILES FIL1,FIL2. THEN FIL2 WOULD BE REFERRED
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TO AS #2. UP TO 16 FILES CAN BE USED IN ONE PROGRAM
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30 INPUT NEW NAME TO BE PRINTED ON FILE.
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40 THIS STATEMENT 'IF END' SETS UP THE IF END
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CONDITION. THIS MEANS THAT WHEN THE FILE PIONTER GETS
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TO THE END OF DATA IN THAT FILE THEN GOTO 85
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50 THIS MEANS TO READ THE FIRST RECORD AND THE
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FIRST ITEM OF THE FILE, IN OTHER WORDS THIS
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THIS SETS THE FILE POINTER BACK TO THE BEGINNING OF THE
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DATA.
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BY USING THIS STATEMENT YOU CAN BE ASSURED OF STARTING
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AT THE BEGINNING OF THE DATA IN THAT FILE
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60 READS DATA FROM FILE#1, SOMEWHAT LIKE THE 'READ' USED
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WITH DATA STATEMENTS.
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85 SETS UP ANOTHER IF END CONDITION TO CHECK FOR THE END OF
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FILE. IF ANOTHER EOF MARKER IS ECOUNTERED THEN GOTO
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LINE 110.
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END-OF-FILE MARKERS ARE DEFINED MORE PRECISELY LATER.
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90 THIS STATEMENT PRINTS THE NEW NAME (A$) ON THE FILE,
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THEN PRINTS AN END OF FILE MARKER ON THE FILE.
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THE END OF FILE MARKER ENABLES THE COMPUTER TO TELL
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THROUGH THE READ STATEMENT (LINE 60) WHEN THE END OF
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DATA IS REACHED
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HERE IS A FLOW CHART OF THAT PROGRAM:
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1. INPUT NEW NAME -----------2. READ DATA FROM FILE
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3. IF END OF FILE #1 THEN 4 -----GO BACK TO 2.
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!
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4. IF END#1 THEN 7
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!
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5. TRY TO PRINT NEW NAME ON FILE, IF SUCCESSFUL (MEANING FILE IS
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NOT FULL) THEN 6. IF UNSECCESSFUL (MEANING FILE IS FULL) THEN 7.
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! !
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!
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! 7. PRINT'FILE FULL'
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6. STOP !
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8. END
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OK, LET'S MOVE ON TO GET A LISTING OF YOUR FILE
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05 DIM A$(20)
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10 FILES FIL1
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20 IF END#1 THEN 70
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30 READ#1,1
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40 READ#1;A$
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50 PRINT A$
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60 GOTO 40
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70 END
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THIS IS A RATHER SIMPLE PROGRAM, IT GOES LIKE THIS;
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YOU SET UP THE IF END CONDITION, THEN READ STARTING AT THE
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BEGINNING OF THE FILE. READ THROUGH THE FILE AND PRINT
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EACH SEPARATE PIECE OF DATA (LINES 40 & 50). WHEN ALL THE
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DATA HAS BEEN READ THROUGH, IT FALLS THROUGH TO LINE 70, BY
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THE CONDITION SET UP IN LINE #20 AND AT THIS POINT
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EXECUTION IS TERMINATED.
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* END OF FILE DISCUSSION *
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HERE IS SOME ELLABORATION ON WHAT YOU HAVE LEARNED SO FAR
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ABOUT BASIC FORMATTED FILES.
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THE EOF MARKER IS WHAT THE IF END CONDITION IS USED
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WITH. THE EOF MARKER DESIGNATES THAT THE END OF DATA HAS BEEN REACHED.
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AS MORE DATA IS PUT INTO A FILE.
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