INKEYS checks the keyboard to see if a key is
being pressed and if so which one. It does not wall
for you to pressa key like INPUT does Itis usually
used in a loop which makes the computer go round
checking the keyboard lots of times. This is
because computers work so guickly. you wouldnt
have a chance of pressing a key in the time ittakes
the computer to do one check.

If you haven't pressed a key before the loop
finishes, the computer carries on with a string
containing nothing (called a "null" string).

NB Apple and VIC do not use INKEY$.

GET is used instead of INKEY$ on VIC and Pet
computers.

GOTO makes the computer jump up or downthe
program ignoring the lines in between. You must
put the number of the line you want ittojumpto
after the GOTO instruction.

GOSUB tells the computer to leave the main
program and go to a sub-routine. GOSUB must be
folowed by the number of the first line of the sub-
routine. At the end of the sub-routine you must have
a RETURN line. This sends the computer backto
the main program to the line immediately following
the GOSUB line. A GOSUB without a RETURN ina
program will give a bug.

IF... THEN tells the computer to decide ifan
expression is true or false, and do different things
depending on the answer. It is used withthe
following signs, and also with AND or OR:

<the same as

< less than

>greater than
< z]less than or the same as
> z greater than or the same as
< >not the same as

Ifthe computer decides an expression is true, it
carries on to do the instruction which follows
THEN. lfit decides it is false, it ignores the restof
that line and goes on to the next one.

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CLS is used to clear everything off the screen
without removing or changing anything in the
memory. lt is useful for removing the listing from
the screenat the beginning of a RUN or ingames
when you want the player to react to something
seen for a limited amount of time. (NB Apple and
VIC do not use CLS - see conversion chart)

HOME is used by Apple computers instead of CLS
to clear the screen. Za

ABS ignores plus and minus signs in frontof
numbers and takes their "absolute" values. E.g.
ABS( — 10)is l0and ABS(-- 10) is also 10.

VAL takes the numeric value of numbers written as
strings. In effect, it tells the computer to ignore the
dollar sign and treat the string as an ordinary
number variable. E.g. if I$—"60" then VAL(1$) isthe
number 60.

ASC converts a character into its ASCII code
number e.g. ASC("3") gives 51. The expression in
brackets must be a string e.g. ASC(A$) or
ASC("20".

NB ZX81 and ZX Spectrum do not use ASC, though
the Spectrum does use the ASCII code.

CODE is used by ZX81 and Spectrum in placeof
ASC. Like ASC it must always be followed bya
string. Remember that the ZX81 uses different code
numbers from the other computers.

TAB moves the cursor across the screentoa
specified column number. It is usually used with
PRINT to display something in the middle ofthe

screen. The number of spaces you want the cursor
moved is put in brackets after TAB. The maximum

number you can use depends on the screen widih
of your computer.

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