Software Engineering Principles

Marks in Paper 1 are not only for output. Structure, naming, efficiency and readability all carry marks, and they're the difference between a pass and a distinction on a working program.

Meaningful identifiers: iTotalMarks, not x. CAPS memos accept Hungarian-style prefixes (iCount, rTotal, sName) but consistency matters more than the convention you pick.
One job per routine: a procedure that reads input AND calculates AND displays is doing three jobs.
No duplicated code: if you've copy-pasted, you probably wanted a procedure or a loop.
Comment the why, not the what: `// VAT is 15% from April 2018` is useful; `// add one to i` is not.
Indent consistently — two spaces per level is the Pascal convention.

Principle	Poor	Better
Naming	a := b * 0.15;	vat := price * VAT_RATE;
Efficiency	Loop always runs to the end	Break out as soon as the item is found
Structure	300 lines in one begin…end	Procedures and functions, each doing one thing
Constants	if mark >= 50 then (twice)	const PASS_MARK = 50;

Code efficiency: No unnecessary duplication — reuse a routine rather than copying it.
Execution efficiency: No unnecessary processing — stop a search the moment you find the answer.
Maintainability: How easily someone else (or you in six months) can change the program safely.

💡 Exam Tip

A PAT mark scheme allocates marks for exactly these things. Renaming your variables sensibly before submitting is one of the cheapest marks available.