Sequence, Selection and Iteration
Constructing and tracing the three core control structures, including nested decisions and count- or condition-controlled loops.
How to study for GCSE Computer Science
Move repeatedly between problem, algorithm, trace, code, test evidence and system explanation; use the exact language and assessment format required by your current board.
Core concepts
Concept 1
Sequence executes operations in a defined order, selection chooses a path from a condition, and iteration repeats a block.
Exam cue: Identify the condition, possible paths and state change before writing control flow.
Concept 2
Count-controlled loops suit a known number of repetitions, while condition-controlled loops depend on program state.
Exam cue: Choose a loop form from whether the repetition count is known in advance.
Concept 3
Nested control structures solve compound problems but require careful attention to scope, indentation and termination.
Exam cue: Prove progress toward termination and test the zero-iteration and final-iteration cases.
Risk pitfalls and guardrails
Updating the loop variable outside the repeated block.
Guardrail: Do not substitute one board's syntax, protocol list, language version or extension topic for the multi-board core; check the current specification and exam year.
Using OR where every validity condition must hold.
Guardrail: Do not substitute one board's syntax, protocol list, language version or extension topic for the multi-board core; check the current specification and exam year.
Writing a condition-controlled loop that never changes the condition.
Guardrail: Do not substitute one board's syntax, protocol list, language version or extension topic for the multi-board core; check the current specification and exam year.
Memory anchors
Sequence
Instructions executed in a specified order.
Selection
A decision that chooses which instructions execute.
Iteration
Repeated execution of a block of instructions.
Count-controlled loop
A loop repeating a known or calculated number of times.
Condition-controlled loop
A loop continuing while or until a condition has a specified value.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
What does sequence mean in an algorithm?
Which construct chooses a path according to a condition?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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