AMSTRAD cpc 6128 User Instruction page 45

.... you can see a number oflines which have to be repeated at various points in the
program, for example the section from line 260 to 31 0. Let's make that section into
a sub-routine and add the instruction RE T URN at the end. Then, we'll call the
sub-routine using the command
GOSUB
260 whenever we want to use it. The
program now looks like this:
10 a=2
15 GOSUB 260
80
I
90 a=5
95.GOSUB 260
160
I
170 a=8
175 GOSUB 260
240
I
250 a=9
255 GOSUB 260
256 END
257
I
260 PRINT "here is the";a;"times tabLe"
270 FOR b=1 TO 12
280 c=a*b
290 PRINT a;"x";b;"=";c
300 NEXT
310 PRINT
315 RETURN
See how-much-tedious_typing we've
sayed_ours~lyeslWell JiesigIlJl(L~mb:l'()utine§
are
a principal part of computing. They lead to 'structured' programs, and develop good
programming habits.
Always bear in mind when writing sub-routines, that you do not necessarily have to
Jump into' the sub-routine at the same point, i.e. its beginning. A sub-routine written
from lines 5 00 to 800 can be called by:
G 0 SUB
5 0 0, or
G 0 SUB
640, or
G 0 SUB
790.
Note in the above program, that the instruction END is used in line 256. Otherwise
the program would naturally continue after line 2 5 5 , and would carry outline 2 60,
which is NOT required unless called by GO SUB.
Chapter 1 Page 32
Foundation Course