Introduction to Algorithms

An algorithm is a finite, ordered set of unambiguous steps that solves a problem. Before you write a single line of Delphi, you should be able to state the steps in plain language — most marks lost in Paper 1 come from coding before the algorithm is clear.

CAPS builds algorithmic thinking through four practices: decomposition (break the problem up), pattern recognition (spot what you've solved before), abstraction (ignore what doesn't matter), and algorithm design (assemble the steps).

Tool	What it's for	When the exam asks for it
IPO table	Separates Input, Processing and Output	Early planning questions; 'identify the inputs'
Flowchart	Shows control flow with standard symbols	'Draw a flowchart to represent…'
Pseudocode	Language-neutral step list	'Write an algorithm…' — do NOT write Delphi here
Trace table	Tracks each variable's value line by line	'Complete the trace table' / 'What is the output?'

Example

Problem: determine the largest of three numbers. Pseudocode: INPUT a, b, c largest ← a IF b > largest THEN largest ← b IF c > largest THEN largest ← c DISPLAY largest

Finite: The algorithm must end — an algorithm that never terminates is not an algorithm.
Unambiguous: Each step has exactly one interpretation. 'Make it nice' is not a step.
Sequence, selection, iteration: The three control structures every algorithm is built from — do this then that; choose a path; repeat.

💡 Exam Tip

When a question says 'write an algorithm', pseudocode earns full marks and Delphi code often doesn't — the examiner is testing whether you can plan, not whether you can type.