Making loops

You often need the coniputer lo do the same thina several umes ina
program On page 2] you can see how to make 1 repeat partola program
asmma GOTOanda variable which acts asa counter Another way is to
TOand

repeat tne same lines several times usina the words FOR
NEXT This is called making a loop

l Hello loop

10 FOR J-l TO 6
(za PRINT "HELLO" ) looP
30 NEXT ]

40 END

This program has a loop from nes l0to
30 which makes the computer repeat
line 20 six times. The letterjisa

vanable and line 10 tells the computer
toset] at l onthefirst run through the
program. 2 the next ume, then 3, etc., up
to 6. Line 20 tells it to print the word

2 Silly sums program

hello and line 30 tells it to go backand

find the next value for]. Whenj-6the

computer goes on to line 40.
—

Loop / Some computers

10 FOR J<1 TO 8 do not havean
% PRINT "2 PLUS 2 IS 5"

and you can
leave itout. |

sum. After doing it eight timesthe
computer carries on with the rest ofthe
program. Line 40 just makes it leavean
empty line.

In tus program, the loop from hnes l0to
30 makes the computer repeat line 20
eight times. Each ume it passes through
hne 20 it prints out the same silly

3 Eight times table program

l0 PRINT "THE EIGHT TIMES TABLE"
20 FOR J<l TO 12
(30 PRINT J.8 Loop
40 NEXT J
50 END

This time ] is used to count the number
ofloops and also as part of the sumJ"8.
Line 20 tells the computer to set] at l,
then 2, 3, ete, up to 12. Line 30 takes the
current value of], multupljes it by 8 and
prints out the answer. Then line 40
sends the computer back to line 20to
find the next value of].

Making patterns

FOR ... NEXTloops are useful for making
patterns, like this, ofa simple shape
repeated lots of times. The program lor
this pattern istoo long to write out herein
full, but it would look something like this:

Steps
Sometimes 1t is useful to change the
may want togoupin sor down in

loop in lines 10 to 40.

Greedy computer program

The 6gure 2 stops the loop after
J<-2(Le. when ihere isone

There are two loops in this program. The
one from lines 101030 makesthe

figure for is printed in line 20. In the loop
trom lines 60 to 80 the computer does no!

Program puzzles
1. Canyoualter the eight times table

on the left to make it display
«| x8<" aswellas the answer?

2. Canyou write a program for the "N"
times table, that is, a program which
works out the tables for any number
youtype into the computer? Firsi yo!

O K.zzz-— HM km kad -—ž-— h

value of] by amounts other than | For instance, you i-—
1s. To do thisyouuse the word STEP. In the following

program STEP -— | makes ] go down by | each time the computer passes throughthe

€. startwith REM (short for remark) are

- -
v v s.

[<1 TO45 H:

10 FOR
20 Draw a rectangle and change its

position a little each time. .
30 NEXT | |
40 END

Some computers %
are slower han J
others and they
need a lower figure
such as 500 or
250 in line 60

have to do anything. Itjust runs through ali
the values for K from | to 1000 and this
makes it pause [or a momenti. Lines whuch

ignored by the computer and are useful to
remind you what the program i5 doing.

need to get the computer to ask you lor
a number, N. Thenuseaa loop to work