Subroutines

A subroutne Isa SOT! ( mini-program withina program ltcairiesoul a
particular task such as adding numbers or keeping aa scote and you can
"nd the computer to it whenever you want lhis task carried out This
-aves writing CU! the program lines each time and makes the program
<korter and easier lo read and type Into the computer

GO OUT OF THE DOOR SE£ SHOPPING

TURN LEFT, LEFT AGAN

Each time you wanted the robot to buy
something you would have to give itthe
same instructions. It would be much
simpler to give the robot a shopping
subroutine and tell it to refer to it each ume.

Suppose you had a robot helper whom
you could program to run errands for you.
you wanted something from the shop
you would have to give it precise
instructions telhng it how to getthere

4 4 Shopping program

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10 PRINT "WHAT DO YOU WANT FROM THE SHOP"
20 INPUT X$ je ZIM Line 30 sends the
30 GOSUB 100 computer to the first
,,40 PRINT "ANYTHING ELSE" | lneofihe subrouune
J 50 INPUT M$ 44A You need the word
s -l Enej THEN GOTO 10 glšii,4 mal program o lop
——— 30, e computer
UPE, th
we, AM —
| 100 REM: SHOP SUBROUTINE | zov
A 4 Hal 110 PRINT "GO OUT, TURN LEFT' ubrouine miha m
MA > 120 PRINT "LEFT AGAIN, ENTER SHOP" obet k la or.
Wllo | PRINT "BUY ';X$;" COME HOME pna
IE 140 computer back to line
Ifyou forgetthe 40 - the hne after

RETURN line you get a bug.

number. The computer automatically
goes back tothe instruction after the one
where it left the main partof the program.

ln BASIC, to tell the computer to gotoa
subroutune you use the word GOSUB with

the word RETURNAat the end ofthe
subroutune. GOSUB should be followed by You can send the computer loa
the number of the first line ofthe subroutine anywhere in the program as

subroutune. RETURN does not need a line many times as you like.

Conversion program
100 INPUT "DISTANCE";M
— m 110 INPUT "TIME,T O...

80 PRINT "A DIVIDED BY B-";AB,. — 130 PRINT "AVERAGE SPEED WAS

9 GOTO 50 Ww 140 PRINT MT." MPH AND":K/T;" KPH"
Z 350 REM: SUBROUTINE TO STOP 150 STOP
/,, 260 IF AO AND B-0 THEN STOP 200 REM: SUBROUTINE TO CONVERT MILES

270 RETURN 210 LET KeMa 1609

RETURN

Numbers program

50 INPUT A
60 INPUT B

Circles program
| Centre ofcircle < X,Y
2 Radius of circle < R

3 Colkur< X
4 Gosub 10 im
5 Gotol

10 Rem: Subroutine to draw circles

This program :s in
English, not BASIC,

ll Draw a circle with centre X,Y;
radius R and colour X.
12 Return

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