Cambridge IGCSE Computer Science 0478: Frequent mistakes

Cambridge Principal Examiner Reports for Computer Science 0478 identify recurring errors in pseudocode, algorithms, theory and exam technique. Mark schemes state they should be read with the Principal Examiner Report for Teachers—common errors and acceptable alternatives are documented there.

Pseudocode and programming

Indentation and structure

Incorrect indentation in pseudocode. Lines within IF/ELSE, REPEAT, FOR structures must be indented to show nesting. Keywords (IF, ELSE, REPEAT) use two spaces; nested statements use four.

Fix: Follow the Cambridge pseudocode guide. Consistent indentation throughout.

Naming conventions

Keywords must be UPPERCASE (IF, REPEAT, PROCEDURE, FUNCTION). Identifiers use PascalCase, start with capital, letters and digits only—no underscores or accented characters.

Fix: IF, ELSE, REPEAT, UNTIL, FOR, WHILE, OUTPUT, INPUT. Identifiers: NumberOfPlayers, not number_of_players.

Data types and syntax

• Integers: denary (5, -3). Real: digits both sides of decimal (0.3, -4.0). Character: single quotes (‘x’). String: double quotes (“text”).
• Missing colons, semicolons or syntax required by the chosen language.

Fix: Use correct literal syntax. Check pseudocode guide for PROCEDURE/FUNCTION parameters and DECLARE.

Variable consistency

Failing to maintain consistent variable names (capitalisation, spelling) throughout. Deleting or not initialising required variables.

Fix: Define variables at start. Use same name throughout. Initialise before use.

Algorithm and logic

Trace and dry-run errors

Errors when tracing algorithms—wrong values in tables; missing steps; incorrect output.

Fix: Work through step by step. Show each variable change. Check loop conditions.

Algorithm design

Incomplete algorithms; wrong logic for the problem; missing edge cases (e.g. empty input, boundary values).

Fix: Read the problem. Plan the logic. Handle edge cases. Test mentally.

Theory and terminology

Imprecise terminology

Confusing related concepts—e.g. “protection from malware” vs. “protection from hacking”. Describing purposes rather than definitions when definitions are asked.

Fix: Malware = malicious software. Hacking = unauthorised access. Define precisely; don’t just describe use.

Insufficient specificity

Vague answers without enough detail. E.g. stating “filter software” without explaining what content it filters (e.g. websites, emails).

Fix: Be specific. Name the concept. Explain what it does. Use syllabus terminology.

Wrong focus

Answering tangential aspects instead of what is explicitly asked. Not reading what information is already provided—leading to redundant or irrelevant responses.

Fix: Underline the question focus. Answer that. Don’t repeat given information unnecessarily.

Exam technique

Time management

Running out of time; failing to complete the paper. Paper 2 (programming) and theory both need allocated time.

Fix: Allocate time by marks. Leave time for longer questions. Practise under timed conditions.

Over-answering short questions

Including unnecessary linked strands in 2–3 mark questions. Fewer, precise points can achieve full marks.

Fix: Match response length to marks. 2 marks = 2 clear points. Quality over quantity.

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Based on Cambridge IGCSE Computer Science 0478 Principal Examiner Reports and pseudocode guide. Check Cambridge past papers for latest reports.