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COMPUTER SCIENCE
WAYS OF REPRESENTING ALGORITHMS
Algorithms can be represented in a variety of ways. We will examine 3 of them here :
1.
narrative
2.
pseudocode
3.
flowcharts
Narrative
This is the use of natural language and natural language rules to construct sentences and paragraphs which
describe the actions to take.
The advantages of a narrative are that
 it can be applied outside of computing,
 It can be understood by most persons and
 It requires no special training to construct
The disadvantages of a narrative are that
 it can be too verbose (too wordy)
 It can be context-sensitive (interpretation varies depending on person’s background and
experience)
Pseudocode
A type of structured English that is used to specify an algorithm.
The advantages of pseudocode are that
 it is independent of a particular language so programmers of different languages can all understand
it
 programmers do not have to worry about syntax
 Lay people can help to determine the validity of the logic because it is not that difficult to
understand
The disadvantages of pseudocode are that
 It is very detailed and so requires a high level of concentration to determine the overall logic
 The loose standards means that one solution may be depicted in several different ways by different
persons
Note the following about writing pseudocode :
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You should give your pseudocode a name and a brief description to indicate what it does
You should list all the variables used and what data type they are.
You must always have start and stop.
Use indentation to help depict the logic
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The control structures are :
• Sequencing
• Input statements - use terms such as input, get, read
• Output statements – use terms such as display, print
• Assignment statements
• Storing a value in a variable e.g. limit  12
• Performing a calculation e.g. sum  sum + num1
• Selection
• IF –THEN
ENDIF
• IF – THEN – ELSE
ENDIF
• Iteration
• FOR loops
• WHILE loops
Program Flowcharts
A diagrammatic representation of the sequence of steps needed to perform a task. They show the sequence
of operations, movements, decisions and storage activities within a system.
The advantage of flowcharts is that
 it is easy to understand by persons at all levels because of the visual nature
The disadvantages of flowcharts are that
 They can become large and unwieldy when the programs are long and complex
 When alterations are required the flowchart will have to be completely redrawn.
 Reproduction: As the flowchart symbols cannot be typed, production of flowcharts becomes a
complex exercise.
Note the following about drawing flowcharts :
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Flowcharts should have a title/label
All flowcharts must have one start and one stop point
Flow lines should run from top to bottom or left to right
Flow lines should not cross
Start symbols have only one flow line going out
Stop symbols have one flow line going in
Decision symbols should have one flow line going in and two coming out
Most other symbols have one line going in and one coming out
Symbols must have the operation written in them
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