Software Engineering for Students A Programming Approach

88 Chapter 7 ■ Structured programming
Figure 7.1 The three structures of structured programming
One view of structured programming is that it holds that programs should only be
built from three components: sequences (normally written in the order in which the
statements are to be executed), selections (normally written as if-then-else), and
repetitions (written as while-do). The goto statement is, by implication, banned. In
this chapter we begin by examining the controversy about the goto statement. The
outcome of the argument is that gotos are an irrelevancy; the argument is about something
else, good program structure. We go on to explore the significant principles of
structured programming.
There are some other principles. We will explore these using flowcharts, which
describe flow of control. A flowchart is read from the top downwards or in the direction
of the arrows. Flowchart decisions (corresponding to if or while statements in
code) are drawn as diamonds. Flowchart activities are shown as rectangular boxes. A
flowchart is very similar to a UML activity diagram and conveys the same information.
If the three structures of structured programming are diagrammed as flowcharts
(Figure 7.1), the following characteristics become clear:
1. they have only one entry and exit
2. none of the constructs consists of more than three boxes
Figure 7.2 A control structure that is not structured