mmary of BASIC

t< section lists some common BASIC words and describes what they

e the computer do and how they are used. Most of them have beenused
tihe programs in this book, so you can check back through the book tosee
wthey work in a game. Notall the words can be used onallthe

nputers mentioned in this book. The conversion chart on page 46 shows

hat you can use instead.

LET tells the computer to label a section ofits
memory and put a particular value in it e.g. LET

A —6 means label a section of memory "A" and put
the value 6init. "A" is calledaa "variable" and putting
something in 1t is called "assigning aa valuetoa
variable".

Some variable labels are followed by a dollar
sign e.g. A$. This means they are for "strings",
which can contain any number of characters,
including letters, numbers and symbols.

PRINT tells the computer to display things onthe
screen and you can use it in several ways:

A message enclosed in guotation marks with
PRINT nn front of it will be displayed on the screen
exactly as you typed it. The section inside guotes
does not have to be in BASIC, it can be anythingyou
lke.

PRINT followed by a variable label e.g. PRINTA
or PRINT A$tells the computer to display the

3 contents of that variable on the screen.

PRINT can also do calculations and then display
the results e.g. PRINT 6" 4 will make the computer
display 24.

You can use PRINT by itself to leave an empty
hne.

RND tells the computer to choose a numberat
random. Different computers use different formsoof
RND and you can see what these are inthe
conversion chart on page 46. On Sinclair computers
| RND by itself produces a number between0 and
b), 99999999, You can vary the limits of the numberit
chooses by multiplying RND and adding to tt. E.g.
RND"20 produces a number between 0and
19.99999999, while RND"'20-- 1 produces a number
between | and 20.99999999.

See INT for how to produce only whole numbers.

See CHR$ for how to produce letters and other
keyboard characters at random.

ga
KT AM

Z]

INT is short for integer, which means whole
number. For positive numbers, tt tells the computer
to ignore everything to the right of the decimal
point. E.g. INT(20.999) is 20. For negative numbers,
it ignores everything to the right of the decimal
point and "increases" the number to the left of it by
one e.g. INT(— 3.6) is —4.

INT is often used with RND, like this:
INT(RND"20 1 1) which tells the computer you want
it to choose a whole number between | and20.

CHR$ converts numbers into letters. Apart fromthe
ZX81, all the computers in this book use the
ASCII" set of keyboard characters in whicheach
character corresponds to a certain number. E.g.
letter A has the code number 65 and PRINT
CHR$(65) will display an A on the screen.
You can use CHR$ with INT and RND to make the
computer select random letters, like this:
CHR$(INT(RND"26 --65))
This line will produce random letters on a ZX
Spectrum (see conversion chart for other
computers).

FOR is used to starta "loop" which will makethe
computer repeat part of a program a certain
number of times. It must be followed by a variable

in a game), and the variable must be given startand
end values (suchas 1] TO 10.)

The end of the loop is marked by a NEXT line
(NEXT G in this example) which increases the value
ofthe variable by l each time and then sendsthe
computer back to the FOR hne again. Whenthe
variable reaches its end value, the computer
ignores the NEXT line and carries on to the line
which follows it. Every FOR must have a NEXTor
you will get a bug.

INPUT labels a space in the computer's memory,
prints a guestion mark and then waits for youto
type something which it can put in thismemory
space. It will not carry on with the rest ofthe
program until you press RETURN, ENTERor
NEWLINE. |

You can use number or string variables with
INPUT, but if you use a number variablethe
computer will not accept letters from you.

« American Standard Code for Information In terchange (see page 45)

-— —