1K INVADERS
Sinclair Programs May 1983
Page 38

THE INVADERS are coming. You are the doomed defender of Earth, bravely
blasting at the overwhelming might of the venomous Venusians. They are
unstoppable but you are determined to litter the skies with their smouldering
carcases. Manoeuvre left and right with 5 and 8 and fire your neutron bolts
with 0.

1K Invaders was written by G Brooks of Knowsley Village, Merseyside.
(1K ZX-81).





ALIEN ATTACK
Sinclair Programs May 1983
Page 52

Yet another alien ship is circling the earth and, once again, it is you who
has the responsibility for saving civilisation as we know it. You have been
provided with a craft which bears a startling resemblance to a giant slug,
which moves relentlessly from side to side.

By pressing 0 you can fire at the spaceship. A hit will be acknowledged on
the screen but the ship remains impervious to attack and the hits serve as
warning shots rather than the usual scenes of destruction and mutilation. The
game continues indefinitely.

The program was written by Mark McLeod for the 1K ZX-81.






AQUA-ATTACK
Sinclair Programs May 1983
Page 47

AQUA-ATTACK is an unpretentious program for the 1K ZX-81. You are a
submariner lurking in the depths of the Atlantic. Your submarine appears
on-screen at random positions and must launch its torpedo, with any key, to
hit the passing passenger ships amidships.

When you succeed there is a satisfying explosion and the number of vessels
which managed to evade your aggressive attentions is indicated alongside.

The program was submitted by Roy Spencer of Ilfrod, Essex.





CALENDAR
Sinclair Programs May 1983
Page 49

If you have a printer and at least a 1K ZX-81, you can make a neat little
calendar with this routine from Simon Kelly of South Croydon, Surrey.

As set up at present, the listing produces a calendar for 1983 but it can be
changed by altering the year in line 20 and the value of Z in line 25. Z
should be made to signify the first day of the year, on the convention that
Sunday equals one, Monday is two, and so on.





CAVE ADVENTURE
Sinclair Programs May 1983
Page 40

Paul Fravigar of Skegness, Lincolnshire has sent an adventure game for the 1K
ZX-81. As you might expect, some of the work has to be done with pencil and
paper and the short initial program must be used to set the random values of
your power reserves and the number of armour and body hits you can sustain.
Your armour naturally must be destroyed before you suffer any body hits. Run
the initial program, lines 5 to 40, note the given values, clear the lines,
then enter the main listing.

As you explore the cave, note the treasure you find and the hits you sustain.
When the damage inflicted by the various monsters is approaching the fatal
level, you should turn and run. The game can be played by more than one
person.





CLIMBER
Sinclair Programs May 1983
Page 29

CLIMBER is a reaction game guaranteed to test the co-ordination of the most
lightning-fingered operator. You must make your way through a series of
parallel walls in which a magical gateway appears at random positions. You
are represented on-screen by A and maoeuvre yourself with keys 1 and 0.

If you are quick enough to position yourself under an opening you can proceed
to the next level by pressing E. When you reach the screen-top your time will
be displayed.

Climber was written by David Cockburn of Manchester. (1K ZX-81).





DIAGONO
Sinclair Programs May 1983
Page 21

Andrew Key of Witney, Oxfordshire, sent Diagono, this intriguing man versus
computer routine for the 16K ZX-81. In conception, it is a kind of low-tech
version of our Program of the Month, requiring you to move the graphic A
across the board from O to O, the loser being the player who is forced to
play into the top right-hand corner. You may move up (I), across (-), or
diagonally (/), illegal moves being rejected.

As listed, the game wis not too difficult but it will certainly interest
readers exploring man/machine interaction.





DODGER
Sinclair Programs May 1983
Page 35

This unusual routine enables you to play that old street-corner routine with
the pea and the three cups. This time, however, you are playing against the
computer and no cheating is allowed.

You have a stake of 100 and are told under which cup the pea is hidden.
Three dots are shown in the centre of the screen and after you have pressed a
key they are moved around according to the difficulty level you have selected.

The difficulty level increases automatically with each gamble. When the cups
have finished moving, enter the position of the pea - 1 to 3 - and the amount
you wish to gamble.

Dodger was written by Tim Grubb of Newton, Linford, Leicester. (16K ZX-81).






FAST DISPLAY
Sinclair Programs May 1983
Page 20

DANIEL FREEMAN of Ramsgate, Kent, writes "On page 12 of the printer manual is
a Basic routine which puts the contents of the screen into the array A$ so
that it can be recalled instantly by using PRINT AT 0,0;A$. Although very
useful, even in FAST mode it takes a long time to RUN. My machine code
version does the same job instantly."

In the listing displayed, the first six lines are the loader listing which
can be put at the beginning of your program and will POKE the machine code
into the REM statement, so that it can be recalled by a line like LET A=USR
16514.

The rest of the listing is a demonstration of what the routine can achieve.
Ten concentric cricles are drawn very slowly and the display saved after
every circle. The computer then replays the pictures at machine code speed.
(16K ZX-81).






HIGH POWERS
Sinclair Programs May 1983
Page 49

HIGH POWERS is designed to avoid the limitations of floating point
arithmetic, which tackles only the first eight significant figures of a
number.

The program enables the user to raise a N to the power P and receive an
answer correct to the last digit. Each digit of the answer is stored in a
single dimension array and, to assist programming, is stored in reverse order.

Line 80 calculates the number of digits in the answer and DIMs D to that
number. Lines 100 to 170 calculate the number, the variable F being used as a
carry. Lines 180 to 240 print-out the final result.

The CHR$ statement in line 230 increases the speed of the printing as the ROM
routine for printiing numbers is very slow. The program occupies only 461
bytes but an expanded machine is required because of the memory needed for
the variables.

High Powers was submitted by J Stephenson of Bolton, Lancashire. (16K ZX-81).





LINK 4
Sinclair Programs May 1983
Page 29

Celia Sims of Gt Yarmouth, Norfolk has managed to squeeze a Link 4 game on to
an unexpanded ZX-81. The display is surprisingly complete, even to the extent
that the counters can be seen falling down-screen into position on the frame.

Link 4 is a version of the parlour game for two people in which you are
required to place four counters in a row before your opponent. In this
listing, the frame for the counters is represented by the numbers 1 to 8 and
you are requested to enter the number appropriate to the column you wish to
occupy.

The four counters can align horizontally, vertically or diagonallly. Black
always leads, so players should take turns in using it.

The listing foes not check for winning lines so it is up to the player to
shout "Yippee" as appropriate. (1K ZX-81).





MINIPEDE
Sinclair Programs May 1983
Page 13

MINIPEDE is a quick and easy program for the 1K ZX-81. You are the
multi-legged insect creeping through the undergrowth, munching the
flavoursome flies (W), crunching the savoury spiders (asterisks) and avoiding
the murderous mushrooms (T).

Score one point for the flies and five for the spiders. Squirm left with the
5, turn right with the 8, and your score will be displayed when you die.

G Creasy of Ashford, Kent, who wrote the program, reports a personal best of 152.





OLYMPICS
Sinclair Programs May 1983
Page 34

PLACE YOUR BETS. This is a foolish but funny listing for the unexpanded ZX-81
which invites you to place bets on a field of knock-kneed athletes competing
in the next Olympics. The runners are represented by an O for their bodies
and an alternate I and X for their lop-sided legs.

Wagers are made by entering your name and the number of the chosen
competitor. There are two input statements, executed one after another, so
that up to eight punters could gamble by using only their initials.

Olympics was written by T Vaskevicus of St Ives, Cornwall. (1K ZX-81).





PLAGUE
Sinclair Programs May 1983
Page 25

PLAGUE is on the difficult side of impossible. You and your eight brave
comrades are attempting to take supplies to a medical team which is battling
to combat an outbreak of mosquito-carried palgue. Unfortunately, a cloud of
the infested insects is hovering between you and your goal.

Use the cursor keys to manoeuvre your men between the deadly flies and if you
manage to reach the medical team and return - unlikely - you will be award 10
points.

As a measure of its difficulty, the author, Denis McCarthy of Todmorden,
Lancashire, has a personal best score of 30. (1K ZX-81).





PONTOON 80
Sinclair Programs May 1983
Page 12

We are becoming short of ZX-80 programs. Are all you oldie owners running out
of steam?

Pontoon 80 does what you would expect, enabling you to play the computer and
other humans. Lines 40 to 80 determine the computer score and are arranged so
that it cannot bust; perhaps readers might be able to find a more equitable
method?

The routine is very straightforward, each player being supplied with prompts
and the computer score being revealed at the end of the game. G Gill of
Westerham, Kent wrote the listing. (1K ZX-80).





RALLY
Sinclair Programs May 1983
Page 38

RALLY is a very traditional type of scrolling race-track game but its
inclusion of machine code will make it of interest to novice programmers.

After entering the listing the program can then be RUN, your car appearing as
V and requiring to be steered to avoid the side of the road and the
occasional obstacles with keys 5 and 8.

The listing was composed by Damon Roberts of Romford, Essex. (1K ZX-81).





SET RAGGED
Sinclair Programs May 1983
Page 47

Peter Beeftink of Calgary, Canada has written a short subroutine to cause any
length of text to be displayed neatly without cutting-off words halfway. The
text must be defined initially as B$ and the routine reached through a GOSUB
command.

The listing checks for a space and ensures that it appears at the end of the
line. (1K ZX-81).





SLUG SLITHERS
Sinclair Programs May 1983
Page 52

Transformed into a slug, you slither down your screen, trying to avoid death
at the hands of the master gardener. The garden has been littered with slug
pellets and the only way to survive is to slither around them, using cursor
keys 5 and 8 to move left and right.

The program was devised by Neil Martin of Callington, Cornwall for the 1K ZX-81.





SYMMETRY
Sinclair Programs May 1983
Page 20

SYMMETRY is a useful subroutine to create a symmetrical pattern, acting as if
a mirror has been placed vertically and horizontally across the screen. The
routine should therefore be useful in creating mazes or crossword puzzles.

Listing 1 is entered first, then RUN; then lines 20 to 80 are deleted and the
following command is then entered: POKE 16510,0. The demonstration program
should then be entered. It will generate random characters at random
positions in the top left-hand quarter, and then echo them at top right,
bottom right and bottom left.

Symmetry was submitted by Paul Mott of Spalding, Lincolnshire. It manipulates
the 16K display file and is therefore unsuitable for the unexpanded machine.
(16K ZX-81).





TAKE OFF
Sinclair Programs May 1983
Page 27

TAKE OFF for the 1K ZX-81, which was sent by C Robinson of Slough, Berkshire
challenges your mathematical speed and accuracy. A rocket is on the launch
pad and time is ticking away. Fuel must be delivered to the rocket along the
underground pipeline by answering 20 questions correctly before the time
reaches zero.

If your skill at subtraction is good enough for the test the rocket will
blast into outer space; if not, it will be left stranded.





ZAPMAN
Sinclair Programs May 1983
Page 19

The SPACMAN craze has spread. Adam Peel of Wylam, Northumberland is the
latest victim of this epidemic and has sent a version of the game for the
ZX-81.

Steer the gobbler round the maze and collect points by consuming dots,
asterisks and ghosts. You can only get the ghosts if your power is above
nought, otherwise you are vulnerable. Your power is decreasing all the time
but you boost it by 15 when you eat an asterisk and your score is also
increased by 10. One score point is gained for every dot demolished.

Finish the phantom and you pull 20 points and win a wraith. The game ends
when a ghost grabs you, when your power is nought, or when you wallop a wall.
Throughout the game your power is displayed; at the end of the game your
score is displayed.

Gobbler is steered with the cursor keys; there are five levels of difficulty
and as the game progresses it becomes more challenging. Zapman was submitted
by Adam Peel of Wylam, Northumberland. (16K ZX-81).
