Software Engineering for Students A Programming Approach

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Exercises
7.1 Review the arguments for and against goto statements and criticize their validity.
Exercises 99
4. the difficulty of finding out where you came from in a program constructed
using gotos
5. the need to read backwards in a program with gotos in it.
6. the difficulty of proving the correctness of programs that use gotos.
The arguments for gotos are:
1. to ban them is to deskill programming
2. they have a use in exceptional circumstances
3. gotos are sometimes necessary in order to make programs perform well
4. it is sometimes “natural” to use gotos.
Much of the debate about structured programming has been conducted in this way.
Throughout the arguments, the need for clarity in programs is the dominant idea.
The avoidance of gotos does not necessarily lead to a structured program. The
central idea of structured programming is abstraction. Indeed, we can define structured
programming as:
“the systematic use of (control) abstraction in programming”
(Abstraction can be applied not just to control, but to data as well. This is the subject
of other chapters.)
Abstraction requires not only the use of suitable control structures but also a systematic
design method.
7.2 State in your own words what structured programming is. Imagine that you meet a
friend who is used to programming using gotos. Explain in simple clear language what
structured programming is.
7.3 A while statement can be used instead of an if statement, because the statement:
if bool then s endif
can be rewritten as:
while bool do s bool = false endwhile
Show how an if-then-else statement can similarly be rewritten using while statements.
If the if statement is superfluous, why have it?