ALIEN (1K ZX-81)
by Peter Coupe
from Home Computing Weekly 4 (29 March - 4 April 1983), page 27

Ten alien space ships are on your tail, and you only have fifteen warheads
left with which to destroy them. Worse still, the more aliens you kill, the
more determined the survivors are to stay alive. Peter Coupe offers some
advice on how to come out on top.

You move the warheads by pressing any of the keys on ZX81. The longer you
hold down a key, the further the warhead travels... but to finish the aliens
off, you have to get within killing distance in only three key depressions.

Line 120 of the program holds the formula for how close you need to get to
the aliens. Try changing it if you find the game too easy - or too hard.



DRAW (1K ZX-81)
by Roland Daw
from Home Computing Weekly 4 (29 March - 4 April 1983), page 27

If you ever owned an Etch-a-Sketch game you will recognise the uses of this
program by Roland Daw, which lets you draw lines and block graphics anywhere
on the screen.

Just nine keys control the functions. 2, 4, 6 and 8 move down, left, right
and up. 1 lets you draw, and 3 lets you erase. 7 will save on tape anything
you have drawn, if you set the cassette on to record before you press it. 9
lets you write an alphanumeric combination at a point on the screen to the
right of the last cursor position. And 0 lets you see exactly where the
cursor is at the time.

This program fits snugly into 1K of memory, and leaves just enough space to
draw in about half the screen.



SUB HUNT (1K ZX-81)
by Bill Butcher
from Home Computing Weekly 4 (29 March - 4 April 1983), page 27

A thousand leagues under the sea... an enemy submarine is out to get you. Try
to torpedo it before it torpedoes you, in this action-packed program by Bill
Butcher.

The enemy sub is hiding somewhere in the 9 x 10 grid on your sonar screen.
You must track it down by entering a row and column number. As you get
closer, the number that comes up on the screen will get lower. To start with,
you have 30 tries; as you get better, try reducing the value of X in line 100
to make the game harder.



VORTEX (1K ZX-81)
by Steve McCallum
from Home Computing Weekly 4 (29 March - 4 April 1983), page 27

Imagine you are the vortex, a hungry monster which lurks in a maze waiting
for unsuspecting creatures to fall into its clutches. To reach safety, your
victims have to reach the bottom of the maze without bumping into you, and if
they do, they win. You have to try to stand in their way - but time is short,
because you only have six tries.

In this adventure game by Steve McCallum, you are represented by the * sign
and the computer takes the part of your victim, represented by the > sign.
You move it yourself in response to its requests: 2 means right, -2 means
left, 9 means down-left and 11 means down-right. But it sometimes makes
mistakes, and if it asks for a move which would take it off the boards, you
have to play fair and move it in the opposite direction.

[To make your move, you must enter one of the following values:

8  = Right
5  = Left
65 = Down-left
68 = Down-right
75 = Up-left
78 = Up-right

]


WIDGETS (1K ZX-81)
by Bill Butcher
from Home Computing Weekly 4 (29 March - 4 April 1983), page 26

You are managing director of an up-and-coming widget producing company. As
the sales figures come in each week you face a tricky business decision: are
you selling enough widgets to put more money into production, or should you
concentrate on advertising to boost sales?

This program by Bill Butcher lets you try your skill at business. Starting
off with 990, you must balance your resources between production and
advertising - but be warned, it's not a good idea to spend more than 5 at a
time on ads!



MASTER CODE (1K ZX-81)
by Derek Sorensen
from Home Computing Weekly 4 (29 March - 4 April 1983), page 43

This classic brain teaser, from Derek Sorensen, pits you against your 1K
ZX81. You've got 10 chances to get the numbers right.

Sharpen up your brain with my Master Code game in which you have to break the
code set by the computer.

It runs on the 1K ZX81 and here are the rules of play:

1  The computer sets the code, which consists of four different numbers from
1 to 6.

2  You must ascertain, initially by guesswork but eventually by logic, what
the code numbers are and in the correct order. You will by given clues as to
the identity and position of the four numbers - an inverse '+' means a number
is correct and in the correct position and a '+' means a number is correct
but not in the correct position.

3  If you successfully break the code then the number of turns you have had
is displayed on the screen.

4  If you take more than 10 attempts then the computer prints the message:
YOU LOSE.


HOW IT WORKS

Line 2 sets up the constant S = 6 saving memory.

3-6 set up variables A, B, C, D, as random numbers from 1 to 6.

7 checks that A, B, C, D are all different. If not, they are re-set.

9 tells player he may begin.

10 and 160 form the FOR-NEXT loop N.

20-50 allow input of player's guess (variables AA, BB, CC, DD).

60 prints player's guess.

70 to 140 print coding from which player may eventually deduce the solution.

150 escapes from the loop if the correct solution is input.

170 prints YOU LOSE if the correct solution is not found in 10 tries.

175 halts the program until Break is pressed.

180 prints number of guesses player had if the correct solution is found.