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V rni book contains simple games

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About This Book

programs to play ona microcomputer.
They are written for use on ZX81, ZX
Spectrum, BBC, VIC 20,
TRS-80 and Pet and Apple micros, and
many are short enoughto fit into the
ZX8]'s IKof memory.

Most micros use the language BASIC,
but they all have their own variations or
dialects. In this book, the main listing for
each program works on the ZX8]1 and
lines which need changing for the other
Computers are marked with symbols and
printed underneath. The fact that the
programs are written for several micros
means that they do not make full use of
each one's facilities. You could try
finding ways of making the programs
shorter and neater for Your micro.

For each game, there are ideas for
changing and adding to the programs
and towards the back ofthe book you
will find tips and hints on writing games
of your own. Also in the bookisa

conversion chart to help youadapt
programs in magazines and other books
for your micro and a summary ofthe
BASIC terms used in this book.

Typing in the programs

Lines which need changing for
computers other than ZX81 are marked

|. with these symbols:

" same symbol and type that in instead.

a VICand Pet
4 BBCand Acorn Electron
e TRS-80
6 Arple
s ZX Spectrum
Every time you see the symbol forthe
micro you are using, look below forthe
7 corresponding line number with the

Points to remember

1 Type the lines exactly as they are printed
includingall punctuation and spaces.

2 Press RETURN, NEWLINE or ENTER
key at the end ofeach program line.

3 Check each line as you go.

4 Make sureyou don't miss out alineor
confuse one with another. A piece of paper
or a ruler is useful to mark your placein
the listing.
9 Look out for the symbols and make Sure
yOu use the correct lines for your
computer.
6 If you are using a ZX81 or ZX Spectrum,
remember not to type the program
instructions letter by letter butto usethe
special key for each instruction instead.
You may find it easier to get someoneto
read the program out to you while you
type itin. Don't forget to explain thatthey
must read every comma, fullstop, bracket
and space and differentiate between letter
"O" andzero, FORand4, and TO and.

Debugging programs

When you havetyped
in the program, check
your manual to find out
how to display it onthe
screen. (Usually you
type LIST followed by
the line numbers ofthe
section you wantto
see.)

VIC 20 versions of all except the graphics program should workon

Pet computers.

e—————o
—

Check you have
typed everything
correctly. It is easy to
make mistakes, so
expect to find some. Use
Your manual to find out

, how to make changesto
» the program once:itiis
typed in. If in doubt, you
can always type the line
again. All the computers
will replace an existing
line with a new one with
the same number.

Here isa checklist of common
mistakes to look out for:
l Line missed out
2 Line wrongly numbered

3 The beginning of one line joined onto
the end ofanother.

especially in long, complicated lines.
Watch for double brackets in particular.
3 Wrongline used for your computer.

6 Letter "O" confused with zero.

1 Wrong numbers used, e.g. extra zeros
included.

Playing the games

To start the game you must type RUN. In

some games things happen very guickly,

so make sure you have readthe
instructions and know what you are
supposed to do.

It is guite likely that the program still

a, či tj ) d
has a mistake in it and either won' ste]
at all or the game won't work property. ič | |
Sometimes your computer will give you
an error code which you can look upin
the manual. This may help you findthe
mistake, though not always. List the
program again and check it carefully
against the book.

When the game is over, the computer
will usually say something like BREAKIN
LINE 200. To play again, you have to type
RUN.

Experimenting with the games

There are suggestions for changing and
adding to the programs throughout the
book, but don't be afraid to experiment
with changes of your own. You can't
damage the computer and you can
always change back to the original ifthe
changes don't work.

You will probably find you want to
adjust the speed of some games, |
especially after you have played thema |
number of times. You will find out which
line to charige on each program page.

Wherever you see
PRINT, you can
change the message in

messages.

Typea line number (say 105 if youwant
to add a message between lines l00and
110), then type PRINT, then your
message inside guotes.

Ifyour computer can make colours
and sounds, you could use your manual
to find out how they work and try adding
them to the games in this book.

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