Nimo

Alyson Bailey takes her first steps with personal computers





Learning to program the Spectrum way





How clever are computers, I wondered, as I unpacked my


first, a Spectrum, two weeks ago. Since then my assessment


of this tiny box, no bigger than an average-sized book, has


varied through "very bright" to "doesn't think for itself"


and "shows great potential".


The manuals which accompanied the new toy were excellent


and we soon had a variety of combinations of BORDER and


PAPER flashing gaily on and off the TV screen, accompanied


by notes of random duration. A clock with a moving hand,


graphs and a design produced with circles of different dia-


meters followed in quick succession. If this was computing,


it was tremendous fun.


It was the youngest member of the family, aged 14, who


noticed the first deficiency. His friends, he said, had


computers which played games and ours did not. So far as we


knew, no software was available for the Spectrum and if we


wanted games we would have to type-in the programs our-


selves. Armed with a selection of computer magazines we set


to work enthusiastically but our enthusiasm soon began to


wane.


The print for some of the programs was too faint to read.


Others, though clearly printed, did not work. Our typing


errors did not help; the computer was amazingly fussy about


punctuation and that had never been one of our strong


points.


Although admitting that some of the failures were our


fault, others, we were convinced, were not. The computer


refused some words like RND(99) and other programs contain-


ing words like CHR and PEEK seemed doomed to failure. PLOT


resulted in miniature graphs in the bottom left-hand corner


of the screen.


What was wrong? Did the computer have a language and per-


haps even a dialect all of its own which prevented it com-


municating with even its closest relatives, the ZX-80 and


ZX-81? Was this ASCII - whatever ASCII is? At long last we


found a program which worked - *Luca* from /Sinclair User/,


June, 1982. Junior added sound and colour and altered the


graphics and what a difference those additions made. Who


complained that the sound was too quiet? Imagine all those


beeps played at the same volume as pop music.


Success was followed by more failures, despite avoiding


programs containing "foreign" words. Had we over-estimated


the powers of understanding of our computer yet again? We


studied the listings. Surely there were mistakes. Should


the letter in one program not be the number 5, the INT in


another be replaced by =; was CLS missing in another?


Several seemed to have whole lines missing while others


had superfluous ones, no doubt relics of bygone versions.


Our computer could not cope with typing errors. Those


errors were human and beyond the mental capacity of the


Spectrum. With errors corrected, those programs produced


several more working games. Why, we asked, do producers of


magazines over-estimate the ability of computers? Surely


experience should have taught them that computers are not


superhuman?


Frustrated by our failures but elated by our ever-


improving ability to understand our computer, we decided to


try to write our own program. We agreed that the concept of


our first attempt must be simple. /Sinclair User/ provided


the basic idea, the game *Nim.* It is a game for two play-


ers who take turns to take any number of matches, up to a


pre-determined value, from a pile of 100. The winner is


the person who takes the last match. We typed-in the basic


game:


100 LET j=100


150 PRINT j


200 INPUT a


300 LET j=j-a


400 PRINT j


500 GO TO 200


and decided to take up to 11 matches and set our program to


RUN. It worked. "That is a bit boring", commented junior,


and I must admit it fell far short of *Space Invaders.*


"Wait", I said, "it will get better". Colour impressed


him, so we added that - line 10 - and moved the numbers to


the centre of the screen - edit lines 150 and 400 - remem-


bering to clear one before the next appeared - line 390.


Running the program produced only a marginally better


response. We added captions, lines 15, 20, 22 - without


"one player and the" - 30, 32, 34, 36; some questions and


demands for answers - lines 40, 50, 60, 65, 70, 75 - let


the computer decide whose turn was next - lines 90, 170,


172 (without "AND bs <>"c""), 210, edit 500 and gave a


choice of number to be subtracted - lines 140, 145.


Then the game was much more interesting but cheating


began to rear its head and had to be eliminated - lines


240, 250. After much thought, I realised how to win and


decided to let the computer take my turn if so requested -


add the remainder of lines 22 and 172 and add lines 24, 67,


175, 190. We also added lines 450, 1000, 1010, 1020, 1030


to announce the winner. Interest soared.


It was at that point that the computer showed human


characteristics. It refused to play if it knew it could be


beaten. Addition of another line - 180 - forced it to


continue playing. Then it could not prevent me winning,


provided my mathematics did not let me down - and fre-


quently they did. Junior complained that the computer won


only because it had second turn. He was given the choice of


first or second turn - lines 72, 95 - but still he lost and


I won. No-one else has beaten the computer and if they do I


will alter the program so that even I cannot win.


All that leads me to wonder who really is my opponent


when I play games against a computer. Is the computer as


intelligent as it appears or am I playing some far-off


programmer I have never met?


Put this program into your computer and see if you can


beat it or me. If you can, try to alter the program to make


the computer win every time. If you succeed you are the


true winner. [All the more so because it's mathematically


impossible to do so - RLB] The computer can achieve no more


than the programmer - or can it? Are you as quick at mathe-


matics? I am not.