ZX Computings - OpenLibra

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The first few weeks after the
purchase of your ZX81 may
justifiably be defined as the
"infatuation" stage. The
power of the machine to
generate data at apparently
phenomenal speed is
fascinating, even exciting to
those new to the computer
keyboard. Scores of little
programs are lovingly saved
on cassette tapes — most of
them centred around the
FOR/NEXT loop. Typical
programs include printing out
"HELLO" 47 times, filling the
screen with nine-digit columns
of sin(x)and —cos(x) or
meaningless equations chosen
primarily for their complexity.
As many of these little morsels
as possible are crammed on
both sides of C60 (or in some
cases even C120!) tapes.
Frantic trips to purchase new
supplies of blank cassettes are
frequently made or, if the
shops are shut, a previously
loved recording of
Beethoven's ninth is
irreverently erased in order to
make room for a program
which generates the first
2000 primes (I often wonder
what you do with primes after
you generate them but they
seem to offer solace to many).
Naming Names
But all things come to an end
at some time or another. It
gradually dawns on most
people that their "collection"
is in reality nothing more than
a heap of rubbish. Most of
what they have saved is
useless, and the few that have
some merit are buried
between dozens of unwanted
remnants.
10
20
30
35
40
50
60
REM PRIME NUMBERS
DIM O(20O0)
LET Z=1
SCROLL
PRINT 2
LET O(l) =2
Organisation, The
Key?
Any attempt to organise your
computing life must begin
with a simple rule . , . one
program on a tape with a copy
on the reverse side.
Superficially, this appears to
be a shocking waste of tape
because, on the average, most
of the tape will remain unused
but in spite of this the rule is
sound in human terms. It is
better to waste a few feet of
relatively inexpensive tape in
return for the following
benefits: no infuriating
searches for programs "in the
middle"; no need to name
FOR G = 3 TO 2000 ST£P
70 FOR H=1
30 IF INT
GOTO 500
100 NEXT H
150 LET Z=Z + 1
200 LET Q(Z)=G
240 SCROLL
250 PRINT G
250 PAUSE 50
50© NEXT G
TO Z
( G.-'tf IHJ > + /.H*
SP
=G THEN
Library
programs, therefore no need
to memorise what you have
named them; if you have to
amend a program, there is no
danger of the extra few bytes
extending into the obliterating
the beginning of the next
program; if the tape is
accidentally dropped into a
plate of soup (or a similar
household hazard degrades its
performance) only one
program is lost; if you lend a
tape to a friend for copying
purposes and it is returned a
corrupted length of jargon,
there is less danger of physical
violence breaking out if only
one program is spoilt.
Finally, we cannot entirely
discard a psychological factor.
Weeks, perhaps even months
of programming work
condensed onto one tape fails
to impress the casual
acquaintance. Spread out into
twenty or so, neatly labelled
cases with the whole resting
in a partitioned "cabinet" will
enhance your local reputation
as an egghead.
worthwhile
Programs
"Worthwhile" in this sense
means "is it worth saving on
tape?" Consider the following
as a reasonable set of criteria
from which to start:
1) Has the program been
tested for every conceivable
input combination. For
example, what happens if you
input a "0" or a negative
number or a number with
umpteen digits in it? Nothing
is more humiliating to a proud
demonstrator than one of
those sarcastic error
messages which leap up from
the bowels of the BASIC
interpreter whenever it suffers
the slightest confusion.
Particularly if you are trying to
impress.
2) Will the program check for
ridiculous input 7 Remember
that an input can be
mathematically acceptable
and free from syntax error but
can stilt lack realism. For
example, let us assume a
program, which assists in the
design of a signal amplifier,
asks for the supply rail
voltage. If the operator
mistakenly keys in 2.6E4
instead of 2.6E 4 will the
stupid machine accept
this ... or what is more to the
point . . . will the stupid
program accept it and go on to
compute a recommended
output current in the order of
kiloamps? In short, does the
program include full data input
validation routines?
3) Is the program completely
self-explanatory to the
operator? Are there, for
instsice, full instructions on
the VDU screen or does it
mean searching for some
scrap of paper somewhere
which contains the gory
details of the button-pressing
routines? No accompanying
document of any kind should
be necessary because the
VDU screen can tell all. There
should also be a title page
which defines clearly the
purpose of the program.
Remember that at the time of
1MER 1382 ZX COMPUTING SUMMER 1982 29