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Library Building library After the first mad programming spree with your machine you may like to build yourself a library of useful programs. 28 ZX COMPUTING SUMMER 1962 Z K jt- I * f> g p f< tr ki P< o rt F< si o IT P' A at b* a Fi si fr st k) B< irr m w 2( w V< se
I sr The first few weeks after the purchase of your ZX81 may justifiably be defined as the "infatuation" stage. The power of the machine to generate data at apparently phenomenal speed is fascinating, even exciting to those new to the computer keyboard. Scores of little programs are lovingly saved on cassette tapes — most of them centred around the FOR/NEXT loop. Typical programs include printing out "HELLO" 47 times, filling the screen with nine-digit columns of sin(x)and —cos(x) or meaningless equations chosen primarily for their complexity. As many of these little morsels as possible are crammed on both sides of C60 (or in some cases even C120!) tapes. Frantic trips to purchase new supplies of blank cassettes are frequently made or, if the shops are shut, a previously loved recording of Beethoven's ninth is irreverently erased in order to make room for a program which generates the first 2000 primes (I often wonder what you do with primes after you generate them but they seem to offer solace to many). Naming Names But all things come to an end at some time or another. It gradually dawns on most people that their "collection" is in reality nothing more than a heap of rubbish. Most of what they have saved is useless, and the few that have some merit are buried between dozens of unwanted remnants. 10 20 30 35 40 50 60 REM PRIME NUMBERS DIM O(20O0) LET Z=1 SCROLL PRINT 2 LET O(l) =2 Organisation, The Key? Any attempt to organise your computing life must begin with a simple rule . , . one program on a tape with a copy on the reverse side. Superficially, this appears to be a shocking waste of tape because, on the average, most of the tape will remain unused but in spite of this the rule is sound in human terms. It is better to waste a few feet of relatively inexpensive tape in return for the following benefits: no infuriating searches for programs "in the middle"; no need to name FOR G = 3 TO 2000 ST£P 70 FOR H=1 30 IF INT GOTO 500 100 NEXT H 150 LET Z=Z + 1 200 LET Q(Z)=G 240 SCROLL 250 PRINT G 250 PAUSE 50 50© NEXT G TO Z ( G.-'tf IHJ > + /.H* SP =G THEN Library programs, therefore no need to memorise what you have named them; if you have to amend a program, there is no danger of the extra few bytes extending into the obliterating the beginning of the next program; if the tape is accidentally dropped into a plate of soup (or a similar household hazard degrades its performance) only one program is lost; if you lend a tape to a friend for copying purposes and it is returned a corrupted length of jargon, there is less danger of physical violence breaking out if only one program is spoilt. Finally, we cannot entirely discard a psychological factor. Weeks, perhaps even months of programming work condensed onto one tape fails to impress the casual acquaintance. Spread out into twenty or so, neatly labelled cases with the whole resting in a partitioned "cabinet" will enhance your local reputation as an egghead. worthwhile Programs "Worthwhile" in this sense means "is it worth saving on tape?" Consider the following as a reasonable set of criteria from which to start: 1) Has the program been tested for every conceivable input combination. For example, what happens if you input a "0" or a negative number or a number with umpteen digits in it? Nothing is more humiliating to a proud demonstrator than one of those sarcastic error messages which leap up from the bowels of the BASIC interpreter whenever it suffers the slightest confusion. Particularly if you are trying to impress. 2) Will the program check for ridiculous input 7 Remember that an input can be mathematically acceptable and free from syntax error but can stilt lack realism. For example, let us assume a program, which assists in the design of a signal amplifier, asks for the supply rail voltage. If the operator mistakenly keys in 2.6E4 instead of 2.6E 4 will the stupid machine accept this ... or what is more to the point . . . will the stupid program accept it and go on to compute a recommended output current in the order of kiloamps? In short, does the program include full data input validation routines? 3) Is the program completely self-explanatory to the operator? Are there, for instsice, full instructions on the VDU screen or does it mean searching for some scrap of paper somewhere which contains the gory details of the button-pressing routines? No accompanying document of any kind should be necessary because the VDU screen can tell all. There should also be a title page which defines clearly the purpose of the program. Remember that at the time of 1MER 1382 ZX COMPUTING SUMMER 1982 29
Page 1 and 2: j Summer Britain's Biggest Magazine
Page 3 and 4: ZX 80/81 HARDWARE/SOFTWARE ZX KEYBO
Page 5 and 6: ZX Computing is published quarterly
Page 7 and 8: 16K-byte RAM pock for massive add-o
Page 9 and 10: The @*?$1!&£@ RAM pack Dear ZX Com
Page 11 and 12: I u < o •0 8 & £T © Benchmarks
Page 14 and 15: 1 1© L" 20 30 IN5 5 0 60 80 9C 100
Page 16 and 17: The Explorer's Guide to the ZX81 IF
Page 18 and 19: Orbit S M King from Bristol takes y
Page 20 and 21: ID 15 20 25 30 35 4G> LBV 5 NMER RE
Page 22 and 23: E" OR Pi="M" THEN GOTO 785 CO)TO 7"
Page 25 and 26: I first became aware of the bug in
Page 27: A. Beasley After using the ZX80 for
Page 31 and 32: i! I are odd jmeone to write a a ta
Page 33 and 34: id (and IC AND )MPUTER" er and >ut
Page 35 and 36: 16K Games Power Boat if you're desp
Page 37 and 38: }RTIO 3RT W J Hfl'.f K E COl T CORj
Page 39 and 40: 1220 \225 230 250 ,L NEED m 270 WAY
Page 41 and 42: IKING >S TO THi 350 >TCARD Ol OF 84
Page 43 and 44: LAD ROM THE AT MRS TO FROM V" ) $5)
Page 45 and 46: int it on the a piece of iuble-side
Page 47 and 48: ie •chin* da add re si | )HL. .FI
Page 49 and 50: Micro This program it fascinating t
Page 51 and 52: 9 S e E k isplay-file we can POKEin
Page 53 and 54: sves ile sre insect is ion*t n lsec
Page 55 and 56: — 32) limiting the firing to ten
Page 57 and 58: Winning Positions COIN COIN BELL BE
Page 59 and 60: REM "OTHELLO" St_GU GOTO 1103 LET 5
Page 61 and 62: lTURES P&P) ITAL iGUE write to IGHT
Page 63 and 64: ms, arid I time you convince somebo
Page 65 and 66: ist for the feel good luct their 5
Page 67 and 68: *t»m Tarshis, Executive Vice Presi
Page 69 and 70: and 2.5 volts. This will produce a
Page 71 and 72: tng of KE, the the his mg ay. cts i
Page 73 and 74: Review Keyboard Review Crofton's Ad
Page 75 and 76: "The hi-res board seems to go to a
Page 77 and 78: Make the most of IK Chopper Squad R
Page 79 and 80:
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51 IF A(2) «* 188 THEN LET A (Z)
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4110 IF (A(Z - 13) = 1 OR A(2 - 13)
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ZX81 HARDWARE 40 KEY KEYBOARD. Kit
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4090 GOTO 9100 5000 GOSUB 9500 5010
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I 1K Games 10 LET 20 LET 30 LET 4-0
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Etchasketch This very short program
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meant the addition to its repertoir
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SYSTEM/MULTIFUNCTION COMMANDS BREAK
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270 280 290 300 310 320 IF IF IF IF
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Make sure you get every issue of ZX
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ZX80 Programs ZX80 fights back Musi
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Catch Avoid being trapped by your s
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Software Orwin strikes again Casset
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ZX81 Software LARGE CHARACTERS REM
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Moving graphics Getting into the Mo
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Specialist Book§ i Choosing progra
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OZJIJL I* » JTA. _ A."--." * rt k
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the new address (in decimal) follow
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WHAT CAN I DO WITH 1K? If your answ
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Compiler A program whose function i
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ZX COMPUTING SUMMER 1982 Computer G
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S-100 Name of a bus or connection s
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After taking your move the computer
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WHAT'S ON NEXT? IN HOBBY ELECTRONIC
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are not lost when the ZX81 is turne
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ZX Users' Club JOIN YOUR USERS' GRO
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