Before designing an algorithm it is important to first understand what the problem is. Algorithms can be designed using pseudocode or a flowchart, and the standard notations of each should be known.

Designing an algorithm

An algorithm is a plan, a logical step-by-step process for solving a problem. Algorithms are normally written as a flowchart or in pseudocode.

The key to any problem-solving task is to guide your thought process. The most useful thing to do is keep asking ‘What if we did it this way?’ Exploring different ways of solving a problem can help to find the best way to solve it.

When designing an algorithm, consider if there is more than one way of solving the problem.

When designing an algorithm there are two main areas to look at:

• the big picture - What is the final goal?
• the individual stages – What hurdles need to be overcome on the way to the goal?

Understanding the problem

Before an algorithm can be designed, it is important to check that the problem is completely understood. There are a number of basic things to know in order to really understand the problem:

• What are the inputs into the problem?
• What will be the outputs of the problem?
• In what order do instructions need to be carried out?
• What decisions need to be made in the problem?
• Are any areas of the problem repeated?

Once these basic things are understood, it is time to design the algorithm.

Pseudocode

Most programs are developed using programming languages. These languages have specific syntax that must be used so that the program will run properly. Pseudocode is not a programming language, it is a simple way of describing a set of instructions that does not have to use specific syntax.

Common pseudocode notation

• INPUT – indicates a user will be inputting something
• OUTPUT – indicates that an output will appear on the screen
• WHILE – a loop (iteration that has a condition at the beginning)
• FOR – a counting loop (iteration)
• REPEAT – UNTIL – a loop (iteration) that has a condition at the end
• IF – THEN – ELSE – a decision (selection) in which a choice is made

any instructions that occur inside a selection or iteration are usually indented

Pseudocode can be used to plan out programs. Planning a program that asks people what the best subject they take is, would look like this in pseudocode:

REPEAT OUTPUT 'What is the best subject you take?' INPUT user inputs the best subject they take STORE the user's input in the answer variable IF answer = 'Computer Science' THEN OUTPUT 'Of course it is!' ELSE OUTPUT 'Try again!' UNTIL answer = 'Computer Science'

Flowcharts

A flowchart is a diagram that represents a set of instructions. Flowcharts normally use standard symbols to represent the different types of instructions. These symbols are used to construct the flowchart and show the step-by-step solution to the problem.

Common flowchart symbols

Using flowcharts

Flowcharts can be used to plan out programs. Planning a program that asks people what the best subject they take is, would look like this as a flowchart:

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