Learn to Program with Small Basic

on line 5 means “run the subroutine named GlumGluffToInch(), and then
return to the line that comes after this subroutine call” (which is line 6 in
this example). It’s like taking a break from cleaning your room to go watch
some TV and then coming back to pick up where you left off. Figure 10-3
shows how a subroutine works in a program.
Main program
TextWindow.Write(...)
glumGluffs = ...
GlumGluffToInch()
TextWindow.WriteLine(...)
Subroutine
Sub GlumGluffToInch
...
EndSub
Figure 10-3: Showing how GlumGuff2.sb calls the GlumGluffToInch() subroutine
Here is one example of output from this program:
How many glum-gluffs? 8.5
That's about 6.38 inches.
A subroutine can access all the variables in the main program, and
the main program can access all the variables in a subroutine. The variable
glumGluffs was created and assigned a value in the main program
(line 3), but it was used by the subroutine to know how many glum-gluffs
it needs to convert (line 12). And the variable inches was created inside
the subroutine (line 12), but the main program reads it and displays its
value to the user (line 6).
Here are some good reasons to put the unit conversion code into a
subroutine:
1. You isolate (or separate) the unit conversion details from the main program.
The main program now doesn’t have to worry about how the conversion
is done. This makes your code easier to read and maintain.
2. If errors occur, you know where to look, which makes debugging much
easier to do.
3. You don’t have to write the same code over and over again! Without
using subroutines, if a program needs to run the same set of statements
more than once, you have to duplicate these statements in your code.
But if you put those statements in a subroutine, you can call it from
any point in your program (code reuse). You’ll practice this in the next
section.
NOTE
In this book, we’ll start the name of a subroutine with a capital letter. We’ll also write
all the subroutines at the bottom of every main program. We recommend you follow
the same practice in your own programs: it’ll help keep you organized!
132 Chapter 10