ROBOTS (ZX-81)
by David Harwood
from Sinclair User 3 (June 1982) page 31

Robots is a variation on the hunting type of game. While appearing simple at
first sight, there is a time limit which introduces a degree of difficulty
to make the game enjoyable.

The object is to erase five robots in a given time, using the cursor. The
formation of the robot means that a fair amount of skill is needed to erase
it, moving the cursor with the normal cursor keys. It is not so difficult,
however, that it cannot be mastered with some practice.

If the robot is not erased in the time given it disappears and another
appears at a random place on the screen. Up to five appear during each game.

Robots requires slightly less than 2K of memory on the ZX-81 and was sent
by David Harwood of Oxford.


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LUCA (ZX-81)
by Matthew Turner
from Sinclair User 3 (June 1982) page 32

Luca is a simple mini-invaders program with only one invader which does not
fire missiles but attempts to destroy you by landing on top of your craft.
The program which fits on to 1K ZX-81 machines uses keys 1 to move your
ship left and key 3 to move it right. Use the zero key to fire but you can
fire only if the invader is directly above you.

The game ends only when the invader manages to land on any part of your
craft. In the meantime, however, each time you repel it by hitting the V at
the centre of the craft you score 10 points.

Luca was submitted by Matthew Turner of Woldingham, Surrey and was one of
the runners-up in the competition in the April issue.


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SQUASH (ZX-81)
by Michael Clark
from Sinclair User 3 (June 1982) page 33

Squash is a simple form of the common amusement arcade games which involve
hitting moving objects with a "bat". It is for one player and the main
attraction is that it can be played on the 1K ZX-81.

The bat is moved from side using the "1" and "0" keys but because the
program is simple the movement is very slow. That can add to the interest
of the game because it is necessary to determine the angles at which the
object is likely to move so as to be in the correct position to hit it.

It was sent by Michael Clark of Rotherham.


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MASTERMIND (ZX-81)
by R Newman
from Sinclair User 3 (June 1982) page 33

Number Mastermind is another variation on the popular Mastermind theme. The
aim is to guess a four digit number chosen at random and the program will
work on a 1K ZX-81.

To use the program just enter your guess in response to the request for
input. Twelve guesses are allowed before you are told the correct answer.
If you want to give up earlier, press NEWLINE.

The accuracy of each guess is indicated by a black peg (shown as the letter
B) for a correct digit in the correct position and a white peg (shown as the
letter W) for a correct digit in the wrong position. For example, if the
number chosen by the computer was 5678, then a guess of 1618 would score BB
and a guess of 1511 would score W.

The program can be made easier by changing line 70. As it stands, each digit
can be 0-9 but if changed to (RND*5+28) each digit would be in the range
zero to four etc.

Number Mastermind was sent by R Newman of Kettering, Northamptonshire.


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HISTOGRAM (ZX-81)
by R Newman
from Sinclair User 3 (June 1982) page 34

Histogram is for a 16K ZX-81 and is a neat example of how to use the
computer to draw bar charts. It can handle up to 28 items of data and its
appearance is helped by the bars being of variable width, according to the
number, so that the available space is best filled.

Bars are produced in two different graphic characters to make them distinct
and there is provision for a heading above the histogram, as well as labels
for the two axes of the graph. Data is scaled automatically to fit the
vertical limits of the screen and any positive numbers can be handled.

A vertical scale, using integer numbers, is drawn automatically at the
left-hand side of the histogram, so that approximate values can be read
from the chart.

The histogram drawing section of the program is in lines 9000-9900, while
lines 100-800 simply get the data required. The histogram routine can be
incorporated into other programs or for plotting more than one set of data.

The data required for the plotting routine is:
  T$, X$, Y$ - title, x-axis label, y-axis label.
  N - number of intervals on horizontal axis.
  Y(1)-Y(N) - data to be plotted.

Histogram was sent by R Newman of Kettering, Northamptonshire.

[There was a spelling mistake in the text 'Characters' within the program]
[histogram in line 440 so I have attached the program as listed and a    ]
[corrected version.                                                 PaulF]


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ZX-IATRIST (ZX-81)
by Dilwyn Jones
from Sinclair User 3 (June 1982) page 37

An interesting concept with a 5K program for the ZX-81 is ZX-Iatrist. Though
the program, so a load and go task is to carry on a kind of conversation
with the user. It recognises a few words and phrases and chooses suitable,
or not so suitable, replies, sometimes making a direct reference to the
statement entered.

The range of words ZX-Iatrist recognises is not great but, as it is based on
very general and commonly-occurring words, there is a good chance that one
of them exists in a sentence.

When run, the program takes two seconds to set up the data for the program so
a load and go routine is included, so that initialisation takes place
immediately. Running the program causes it first to ask for your name and
then compliments or insults you, depending on whim, and when the conversation
starts, you enter your reply, comment or question.

Brief sentences are better, as they run faster. The program scans the
sentence for words it recognises by extracting substrings from K$ and when
it finds a match selects a suitable reply substring from R$.

If the last character of the reply substring is a space it tells the
computer that more information is needed to finish the reply and that is
extracted from the sentence you entered.

The entire reply may take anything from one second to half a minute to
appear. You can reduce that time by switching the program from slow to fast
and back again at certain points in the program, if you do not mind losing
the screen for a time. To install this add the following lines:

95 FAST
20 SLOW
21 INPUT A$

When entering the listing, take particular care with lines 560-660 and
especially with lines 610 and 620, where the amount and position of the
spaces is critical.

ZX-Iatrist was sent by Dilwyn Jones of Bangor, North Wales as an entry in
the competition.


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TRIDENT (ZX-81)
by Charles Kinnear
from Sinclair User 3 (June 1982) page 38

Trident is a simple but interesting game for the 1K ZX-81. It involves
firing a missile at a target. The player chooses the angle and speed at
which the missile will be fired and it remains until the target is hit.

When that happens, the number of shots taken is shown on the screen and the
game is repeated, using a different target. It is easy to appreciate the
idea behind the game but it demands sufficient skill and has enough
combinations of angles and speed to maintain interest.

It was a runner-up in the April printer competition and was submitted by
Charles Kinnear of Kirkcudbright.