SGN tells the computer to hnd out the sign ofa
Ta. number ltproduces | foranegative number,0
Z] iorzeroand - | for positive numbers E g
7 SGN(-30)is - 1, SGN(7)is - landSGN(0)isO0.

DIM tells the computer how much memory space
will be needed for an "array (aroworagrid) E.g
DIM X(6) tells the computer to set aside anarea
large enough to containa row of 6elements and
labelled X DIM A(8,8) means a memory space
labelled A and big enough to take 8elements
across and 8 down is needed The numberof
elements of data used in the program must
correspond to the numbers in brackets after DIM
Or you will get a bug.

SOR takes sguare roots of numbers E.g. SOR(16)
gives the answer 4

SIN calculates the sine ofanangle lna night-angled

tnangle the length of the side opposite an angle

divided by the length ofthe hypotenuse (the side

Ee — Oopposite the right angle) is the sine of that angle

zija teb When you use SIN ina program. the angle youare
ge. using it with must be measured in radians not
degrees

tm zma A,

ATN is one of the trig. funcuons which computers
Can calculate (see also SIN above). It stands for
arctangent and 1t ls important to remember that it
gives an answer in radians, not degrees. Youwill
need to use a maths book to find out how this works
if you do not already know about it.

3

|

STOP rells the computer not to go any furtherina

program. Computers other than the ZX81 canuse
END instead

PEEKisawayof hnding out what is in a specific
area of the computer's memory. You need touse:it

with a number which specifies an "address" inthe
memory.

NB not used on BBC.

POKE isa special way of puttung information inthe

Somputer s memory by usmg a memory "address"
NB not used on BBC

ASCII chart ZX81 code chart

Code ZX81 Code ZX81
number (|character| number |character

don a
rk bes— b— in —- —
I—I—E- N——

Me ao
jr — lupe bor— s — —
o A o ci k. NI MC pi Pe
O PREMA — a —
is—— —i— I— HB ———
/
FM PNE! i ME di ei | 1 ua ME
r—|i — pa — M— [s— —
S —— ES —S— DE —5—
a
EPAR MOPTNEI NJENI S ZEN NE IUIO GENI
ea ee ——) KRE TE
Ee drn ba k —] STE Z
romi ura remo meu Nu ai Km
SEJI IE IE me | VR am
se Pirs (V 5] (Mr
K DROUEE (1 KOD ENE NEUE ENE
K INEME Reci LC ei. ze Nr ai TN
Poraja PX—  |l3I -|9
SS —E—EE—-I— [s—A—
je o je mm (2 | imele —
Mi |e Time] — PLES oe

Chart of screen sizes

Max. number of
characters across
(or number of columns)

ViC20 ua uk nu
TRS-80 PM vak
z 20/40/80

Max. number of
lines down
(or number of rows)

.——