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Good Programs
There are a number of facets to good programs: they must
- run correctly
- run efficiently
- be easy to read and understand
- be easy to debug and
- be easy to modify.
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| What does
correct mean? We need to have some formal
notion of the meaning of correct: thus we define it to mean
| "run in accordance with the specifications".
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| The first of these is obvious - programs which don't
run correctly are clearly of little use. "Efficiently" is usually
understood to mean in the minimum time - but occasionally there will be
other constraints, such as memory use, which will be paramount. As will
be demonstrated later, better running times will generally be obtained
from use of the most appropriate data structures
and algorithms, rather than through
"hacking", i.e. removing a few statements by some clever coding - or
even worse, programming in assembler!
This course will focus on fundamental issues in programming and one
of them is solving problems efficiently: you will be introduced to a
number of fundamental data structures and algorithms for manipulating
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The importance of the other points is less obvious. The early history of many
computer installations is, however, testimony to their importance. Many studies
have quantified the enormous costs of failing to build software systems that had
all the characteristics listed. (A classic reference is Boehm's text, B.J.
Boehm, "Software Engineering Economics", Prentice-Hall, 1981 ) Unfortunately,
much recent evidence suggests that these principles are still not well
understood! The discipline of software engineering is
concerned with building large software systems which perform as their users
expected, are reliable and easy to maintain. This course will introduce some
basic software engineering principles but we will concentrate on the creation of
small programs only. By using well-known, efficient techniques for solving
problems, not only do you produce correct and fast programs in the minimum time,
but you make your programs easier to modify. Another software engineer will find
it much simpler to work with a well-known solution than something that has been
hacked together and "looks a bit like" some textbook algorithm.
The discipline of Software Engineering was founded when it was
discovered that large numbers of software projects
- exceeded their budgets
- were late
- were riddled with errors and
- did not satisfy their users' needs.
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