Designing Algorithms (Cambridge International IGCSE Computer Science)

What is an algorithm?

Exam Hint Cambridge IGCSE 0478 assesses your ability to understand, write, and interpret algorithms using pseudocode, flowcharts, and structured design. This page gives examples in the format and style seen in Paper 2, focusing only on examinable methods.

• An algorithm is precise set of rules or instructions to solve a specific problem or task

• There are three main ways to design an algorithm

  • Structure diagrams
  • Flowchart
  • Pseudocode

Structure Diagrams

Spec point — "c) Use different methods to design and construct a solution to a problem"

Structure Diagrams

What is a structure diagram?

• Structure diagrams show hierarchical top-down design in a visual form
• Each problem is divided into sub-problems and each sub-problem divided into further sub-problems
• At each level the problem is broken down into more detailed tasks that can be implemented using a single subroutine

• an example of a structure diagram for a mobile application could be:

Flowcharts

Spec point — "c) Use different methods to design and construct a solution to a problem"

Flowcharts

What is a flowchart?

• Flowcharts are a visual tool that uses shapes to represent different functions to describe an algorithm
• Flowcharts show the data that is input and output, the processes that take place and any decisions or repetition
• Lines are used to show the flow of control

Example

• The casino would like the algorithm refined so that the user also enters their first name and this is used to greet the user when they access the site

Pseudocode

Spec point — "c) Use different methods to design and construct a solution to a problem"

Pseudocode

What is pseudocode?

• Pseudocode is a text-based tool that uses short English words/statements to describe an algorithm
• Pseudocode is more structured than writing sentences in English but is very flexible

Example

• A casino would like a program that asks users to enter an age, if they are 18 or over they can enter the site, if not then they are given a suitable message

Exam Hint Pseudocode is not real code—don’t use syntax like print() or input() with brackets. Stick to simple statements like:

INPUT Age

OUTPUT "Welcome"

Adding actual language syntax can lose you marks.

• The casino would like the algorithm refined so that the user also enters their first name and this is used to greet the user when they access the site

Exam Hint If the question asks you to write an algorithm, default to pseudocode. Use flowcharts only when asked or when visual logic helps. Examiners reward clarity, not decoration.