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ZX81 club Dear Editor, In March of this year one of your rival magazines printed an appeal, by myself, for ZX81 owners and users to contact me if they were interested in establishing a ZX81 postal users club. Over two dozen people replied (including one each from Canada, Germany, New Zealand and Sweden), this ex cellent response has resulted in tentative steps being taken to form such a club. Facilities and services which we hope to be able to provide include: address exchange, discount software (over 50 titles at less than £3.00 each!), International and Junior sections, newsletter etc. Therefore, I would like toask. through your columns, that ALL ZX81 owners and users, who would be interested in joining a club EXCLUSIVELY for themselves, please write to me at the above address, for further infor mation and a questionnaire. Would all respondents please be kind enough to enclose a stamped addressed envelope or an international reply coupon. Many thanks! Yours sincerely lain Dale 78 Cobden St, Thornaby, Stockton on Tees, Cleveland TS17 7 ET Strathclyde club Dear ZX Computing, I am starting a new, nationwide Sinclair User Club. Each week I will send members a newsletter which will consist of games reviews, tips, short routines, discount computer games and more. The cost of membership will be: Spectrum —CIO per year or£ 1 per month. ZX81 - £5 per year or £0.50 per month. Your money will contribute towards postage, discount games tapes and to any other surprises that may appear in the newsletter. I think you will find the iub good value for money, but if you don't enjoy it you will have a money back guarantee for the first two months. If you are interested please contact: Ian Kennedy 24 Waverley Crescent Lanark, Scotland. Spain Hello friends of ZX Computing I am the president of the programmers club of Castellon (Spain), and I would like to know people from all over the world who own Sinclair, Commodore or Astra computers. We (the members of the clubl want to exchange ideas, programs etc without any financial interest involved. Our address is: Jose Manual Martin Sautos Spdo 635, Castellon Spain. CLUB NEWS Penpal - • Dear ZX Computing I am fourteen years old, and would like a penpal who has a Spectrum 48K. I have an Interface 2 and joystick for my Spec trum 48 K, Yours faithfully G. Bent ham PO Box 73 Ngodwana, N.E. Transvaal RSA 1209 While we're on the subject of S. Africa, we've had a letter from a Peter Hup ton, and also from the 'ZX Mushroom Club', both of whom are looking for penpals/ new members but didn't send in their full addresses. So if they're reading this and would like to write again with their addresses, we'd be happy to publish their letters. France Dear ZX Computing I would be very pleased if you would publish this letter. I am French and live near Paris, and I own a 48K Spectrum. I would like to become a member of a Spectrum club as I would like to exchange ideas, news and programs with British users. If there are any clubs that correspond with French or Euro pean users, please write to me at the address below. Yours faithfully Pajard Jerome 57 Rue Segoffin 92 400 Camberoie France Eire Dear ZXC I would like to tell any of your North Kildare readers that I hope to form a small club of Spectrum owners. Anybody in the area who is interested may write to me, enclosing s.a.e., or phone after 7pm at (045)68144 . Yours sincerely Owen O'Connor Downings North Prosperous Co. Kildare, Eire 116 ZX COMPUTING DECEMBER JANUARY 1985
Getting a program typed in is often only the start of your problems. Ed to the rescue. Typing in a program is a useful exercise. Apart from the pa tience required, techniques learned and the end program to be used, probably the most educational part of it is tracking down the bugs introduced by yourself or occasionally by our publication system. In debugging you gain a much deeper insight and understanding on how the program actually works than by merely typing it in, but tracking down these errors is an art in itself and needs some skill. So here are some tips to help you in your efforts when faced with that cryptic error report! 1 NEXT without FOR Look back through the program, either the loop has not been set up - no related FOR 'letter' = No1 TO No2 line, or the letter has been re-used as an ordinary variable within the loop with a LET 'letter' = No. 2 Variable not found This is one of the most common errors. Again, the problem may not lie in the line where the error was detected and reported. If there is only one variable, which may be one or more letters or a string {$) variable, then that is the problem. There may be more than one variable in the line section reported and you will have to identify the offending one. In a line PRINT AT Y,X;A$ the culprit could be Y or X or A$. To find out which of them is causing the problem (it may be more than one! type in turn as a direct command: PRINT Y Enter/Newline PRINT X Enter/Newline PRINT A$ Enter/Newline Note which produces the error report. Now look back through the program printout for the line which sets it up — usually a LET or FOR command. Did you leave it out? Does the program get there or has a GOTO/GOSUB been wrongly addressed? 117 ZX COMPUTING DECEMBER/JANUARY 1985 I 3 Subscript wrong Connected with DIM A(No) or DIM A$(Nol. If the number in the brackets on the line where the error is reported is greater than the one in the original DIM statement, is not an integer or is less than 1, then this report is generated. If the subscript number in brackets - is a number then check and change, however, if it is a variable then follow the procedure for tracing variables. It has probably exceeded the limits, look for lines with the variable being altered with + * / : if necessary add limiting code. For example: IF X >10 THEN LET X- 10 4 Out of memory As well as for programs which are too big, it may happen if the previous program set RAMtop. Before despairing, enter CLEAR USR "a" 1 on the Spectrum: on the ZX81 SAVE the program, turn the machine off and on, then reload the program. 7 RETURN without GOSUB Somehow the computer has reached a RETURN command other than via a GOSUB instruction. Check a GOTO hasn't been entered in place of a GOSUB. Check for a missing GOSUB. B Integer out of range An integer (whole number) either as a number of variable is too big or small and you are attempting to do something like PRINT AT 0,33 - not allowed! Check any variables involved as per report 2 and trace it back through the program looking for adjustments to it by + * / : Add limiting code if needed — see report 3 E Out of DATA A Spectrum problem. Check the number of DATA items match the number of READs; usually one (or more) has been missed out. Attempting to reread a DATA list without first using a RESTORE command will cause this and it can happen on an auto start program (saved with a LINE number). Good programming usually RESTORES to the correct line number before using READ. I FOR without NEXT See report 1 but this time the NEXT is missing! Note that the letters I have used for examples could by ANY letters not just A$,X,Y etc and depend on the particular choice of the programmer. This is by no means a comprehensive list but I have tried to cover many of the most common error reports. Personally, I get almost as much satisfaction from debugging as I do from programming I do assure you, however, that there is absolutely no truth in the rumour that we deliberately inject bugs into our listings in order to introduce you to the dubious delights of
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The Magazine For All Sinclair users
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welcome Ray says hello. Editor: Ray
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At last as we all knew would happen
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short visit my Spectrum was working
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A letter from Eclipse Software SHOP
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Framed The Gordon Microframe is one
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HARDWARE Getting into Print through
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IHARDWARE REVIEW QL Delta Disk Ray
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HARDWARE The Spectrum Beta Plus Dis
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USA NEWS Across the Pond by Mark L.
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QL HARDWARE Micro Peripherals QL Di
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(SPECTRUM GRAPHICS! Screen Master F
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top of the display in such a way th
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ZE USR ST: RETURN 1670 RANDOMIZE US
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3^30 LET G*=INKEY
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Animation is the process that puts
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10 REM CUBOID DRAWING 20 LET OX-=30
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(SPECTRUM GRAPHICS! Spirogram Movin
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FF6B 31 FF6C B9 FP6D 01 FF6E EB FF6
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As we see this old year out and wel
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zapping Your Graphics zx looks at s
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Light Screen Part Nine: by Toni Bak
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Overall then, it would seem that th
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JA01EJ je FE|0 JOBJ )»1EJ 18AP FSO
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^ m HARDWARE — The Perfect Keyboa
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the wrong size and pressure. It loo
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BINARY AND HEX Binary and Hex The A
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Yes, of course, and in exactly the
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SOUNDS speakeasy Kai Webber has com
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IU 9 RECORD MODE 20 ORG 32768 SOUND
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JURY we, the jury Daley Thompson's
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The Rats Hodderand Stoughton £7.95
Page 66 and 67: SOUNDS The Sound Of Music John Ains
Page 68 and 69: +5V Figure 1 Diagram of 'he 8912 PS
Page 70 and 71: SOUNDS HEX DISASSEMBLY OF *C0MMRH0S
Page 72 and 73: F8E4 030F 1710 OUT .« FAE6 23 FRE7
Page 74 and 75: Harwood's Hypothesis This month we
Page 76 and 77: ZX81SCENE ZX81 Chatterbox Julian Ch
Page 78 and 79: OL into The Archive The QL's flexib
Page 80 and 81: endproc proc search_file seek find
Page 82 and 83: EDUCATIONAL REVIEWS Mike Edmunds gr
Page 84 and 85: Anthony Marlow from Cheshire has se
Page 86 and 87: 0« , o < SANTA'S CAME Derek Mearns
Page 88 and 89: 199 RETURN "PI0 REM SCREEN 1 902 BR
Page 90 and 91: 1 , X} INK 2J »F« •: FOR F-L TO
Page 92 and 93: k / , %* ' Id W Y f t t il / V /„
Page 94 and 95: The lure of thai yellow stuff, I ca
Page 96 and 97: 96 1730 IF CDODR THEN GO TO 4000 19
Page 98 and 99: SPECTRUM GAME Pim Quakkelaar gives
Page 100 and 101: Z": FOR z=l TO LEN z*: PRINT AT 8,z
Page 102 and 103: + .3) 2420 NEXT r 2425 IF b(t,1) =b
Page 104 and 105: 18! PRINT AT 1, 11 "H"1 AT 2,t|"_I"
Page 106 and 107: i a a • • • • w !.V. fflf W
Page 108 and 109: ZX81 STRATEGY 321 I F Di = 3 THEN G
Page 110 and 111: 110 34.40 NEXT -5 LE (3 ; i:• = a
Page 112 and 113: HARDWARE REVIE Derek Mearns has bee
Page 114 and 115: IF YOU USE YOUR COMPUTER TO PLAY GA
Page 118 and 119: Conversion (PROGRAMMING TIPS) tips
Page 120 and 121: Lineage: 40p per word E 3 Semi disp
Page 122 and 123: SPECTRUM RGB OUTPUT MODULE THE LEAD
Page 124: SPECTRUM AMSTRAD Jl\0_l_ sales dept
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