RADIOACTIVE DECAY SIMULATION
----------------------------
by D Noonan
from Sinclair User, November 1982

THIS PROGRAM simulates the random decay of atoms. When run, it displays 256
atoms and a bar chart; as one atom decays, a new one is born. The bar chart
keeps a record of the number of mother and daughter atoms. Every decay is
also marked by a burst of sound. The rate should slow if the decay is random.

Following the decay of the final atom you are asked to guess the half-life of
the atom. Your standing as a nuclear scientist is then analysed and you are
told how close you were to the answer.

Radioactive Decay was sent by D Noonan, of London N8.



PROBABILITY (ZX-81)
by Eric Dobbie
from Sinclair User 8 (November 1982), page 41

Poisson's formula is a method of calculating the possibilities of the
recurrence of an event, based on the number of occurrences in the past.

For this listing, the time should be adjusted so that the number of
occurrences is in the range 3 to 12. The range could be extended upwards if
required, but 2 has been omitted as it would mean an unreliably small sample.

The formula here is applied with a correction factor but that will not
distort the results, since the same percentage is applied to all answers,
thus keeping them in the same proportion.

Submitted by Eric Dobbie of Gainsborough, Lincolnshire, for the ZX-81.



TENNIS FOR TWO (ZX-81)
by A Mehmood
from Sinclair User 8 (November 1982), page 42

Tennis For Two is one of the few games for the 16K ZX-81 which can be played
by two people. The display shows an aerial view of a tennis court. Player one
controls his racquet with keys 1 and Z and attempts to drive the ball back
across the net. If he misses  and the ball has a built-in wobble factor  he
loses one of his three lives. Player two responds in kind, though he uses
keys 0 and ".".

An interesting concept, though we found the randomised ball a little too
difficult, Sent by A Mehmood, of Barking, Essex.



LINK FOUR (ZX-81)
by R J Ross
from Sinclair User 8 (November 1982), page 43

Line Four is one of those games for people who prefer thinking thinking to
reacting. It is a version of a popular parlour game for two players which
requires you to try to complete a line of four counters. Your opponent
naturally will try to block your efforts and build his own line.

A diverting game for the expanded ZX-81 from R J Ross, of Clacton-on-Sea,
Essex.



MATCHSTICKS (ZX-81)
by M de Gentile Williams
from Sinclair User 8 (November 1982), page 44

Matchsticks is yet another version of the ubiquitous Last Matchstick game,
the idea of which  as you and your grandmother and the family dog probably
know already  is to make sure that you are not the one to take the last
match.

The novelty of this listing is that it incorporates a tricky little routine
which renders the computer unbeatable  very useful for impressing the
non-Sinclair-owning friend.

Submitted for the expanded ZX-81 by M de Gentile Williams, of London W4.



SPELL (ZX-81)
by S Mosely
from Sinclair User 8 (November 1982), page 44

We have a weakness for educational programs. Spell is a routine for the
unexpanded ZX-81 which requires the student to copy correctly the spelling of
a word which has been flashed briefly on to the screen.

The words are selected by the instructor and can be of any length; therefore
they can be selected according to the age and ability of the child. The
difficulty level could be adjusted further by altering the PAUSE in line 230.

The listing as printed is efficient but perhaps rather stark and might
benefit from a few graphics to congratulate or commiserate, as appropriate.

Submitted by S Mosely of Peterborough.



SMASH AND GRAB (ZX-81)
by Peter Wylie
from Sinclair User 8 (November 1982), page 45

Elbows were flying in front of the office keyboard, jostling to try Smash and
Grab, an annoyingly addictive game for the 16K ZX-81. Superficially it is
like a thousand other games. You are driving around an obstacle-filled arena,
scoring for every  you can hit and losing one of your five lives for every
collision.

The snag is that your vehicle travels only in circles or at tangents,
depending whether or not the 5 or 8 key is being pressed.

Clear all the s from one sheet and you can play again with double the number
of obstacles to avoid. There is a name and high-score routine to tempt your
ambition.

The sender of this diverting game, Peter Wylie, of Christchurch, Dorset,
boasts a personal best score of 5,000. Your reviewer could do nothing to
rival that.



PAC MAN (ZX-81)
by John Watkins
from Sinclair User 8 (November 1982), page 48

This is a Pacman game without the ghosts. Your task is to consume as many
food pellets as possible in the given time. The display is excellent, though
a race against time is obviously less exciting than a race against a ghoulish
death.

The Pacman is manoeuvred right with key 0, left with B, up with Q and down
with Z. Dots are worth one point and asterisks 10. You have one minute 15
seconds to eat as much as possible.

The program was submitted by John Watkins, of Andover, Hampshire, for the 16K
ZX-81. He reports a top score of 267. Perhaps a reader can conjure a little
of the supernatural to add to this routine.



MARK DATA (ZX-81)
by David Stevenson
from Sinclair User 8 (November 1982), page 51

Scottish schoolboy wins printer and 64K Memopak for system which stores and
sorts examination results, based on an idea from one of his teachers

Education theme for winning 48K program

Finding a practical use for the ZX-81 in education was the basis for the
winning entry in our July competition. We asked for a program which would
require 48K of RAM and David Stevenson used it for storing and sorting
examination results. His program, which we list, wins him a Sinclair ZX
printer and a 64K Memopak.

Sixteen-year-old Stevenson said that the idea for the program was provided by
one of his masters at Stranraer Academy, where he is now studying for his
highers.

"I was talking to one of the masters and he said that he wanted a program to
sort examination results, so I set out to write it, partly at home and partly
at school." says Stevenson, of Fairmile, Brookfield Crescent, Stranraer.

The program uses a machine code routine, which is entered at the beginning,
to do the sorting and allows about 350 names and information to be entered in
16K, or more than 1,000 in 48K. It is menu-driven with six options - reading
the files; working-out the average mark; sorting and displaying in
alphabetical order and order of merit; amending the files; and storing them
on tape.

On each entry there is room for the name, the class and the mark for a
particular examination.

Stevenson's interest in computers began about two years ago when the school
started a computer club with a Commodore Pet. The club now has five Pets and
one ZX-81.

In the last year he has tended to use the Sinclair machine more than the Pet.
He has a ZX-81 at home and also prefers the version of Basic and thinks the
system of syntax errors makes it easier to use.

"After taking my highers I hope to go to university to study computer science
and hope to be able to take an O level in computing before I leave." he adds.


 MACHINE CODE
This machine code for the program was not published in the
magazine article. The following was reconstructed by examining the visible
codes in the program listing and then working out the appropriate
instructions for any ambiguous codes.

[see SU8211w008051MarkData.ASM]
