programming-for-dummies

Planning Ahead with Structured Programming 33
Spaghetti programming with the GOTO Command
Although you can write spaghetti programs in
any language, the BASIC programming language
is most closely associated with
spaghetti programming. Early versions of
BASIC used a GOTO command, which essentially
told the computer to “go to” another part
of the program.
The problem with the GOTO command was that
it could tell the computer to “go to” any part of
the program. If you had a large program that
consisted of several hundred (or several thousand)
lines of code, the GOTO command could
tell the computer to jump from one part of the
program to another in any order, as the following
BASIC program shows:
10 GOTO 50
20 PRINT “This line prints
second.”
30 END
40 GOTO 20
50 PRINT “This prints first.”
60 GOTO 40
Line 10 (the first line) tells the computer to “go
to” line 50.
Line 50 tells the computer to print, This
prints first. on-screen. After the computer
follows this command, it automatically
runs the next command below it, which is line 60.
Line 60 tells the computer to “go to” line 40.
Line 40 tells the computer to “go to” line 20.
Line 20 tells the computer to print, This line
prints second. After the computer follows
this command, it automatically follows the
command on the next line, which is line 30.
Line 30 tells the computer this is the end of the
program.
Even though this program consists of six lines,
you can already see how the GOTO command
makes the computer jump around, so it’s hard
to understand how this program works. Now
imagine this program multiplied by over several
hundred lines of code, and you can see how
spaghetti programming can make reading,
understanding, and modifying even the simplest
program much harder.
Book I
Chapter 2
Different Methods
for Writing
Programs
The three parts of structured programming
To keep programs organized, structured programming teaches programmers
that any program can be divided into three distinct parts:
✦ Sequences
✦ Branches
✦ Loops
Sequences
Sequences are simply groups of commands that the computer follows one
after another. Most simple programs just consist of a list of commands that
the computer follows from start to finish, as shown in Figure 2-2.