2.1 · Pseudocode

Goal: read and write pseudocode using HKEAA conventions.

What pseudocode is

Pseudocode is an informal, English-like description of an algorithm. It is language-agnostic — you can later implement it in Python, C++, Pascal or any other language.

HKEAA-style conventions

Convention	Example
Assignment uses ← not =	total ← 0
Comparison uses = (no ==)	IF age = 17 THEN
Keywords in CAPS	IF, THEN, ELSE, FOR, WHILE, END FOR, END IF
Indentation shows block structure	(no braces, no colons)
Comments start with //	// initialise counter

A complete example

// Compute the sum 1+2+…+n
INPUT n
total ← 0
FOR i ← 1 TO n
    total ← total + i
END FOR
OUTPUT total

Common keywords

Keyword	Use
INPUT x	Read a value into variable x
OUTPUT x	Display x
IF cond THEN … ELSE IF … ELSE … END IF	Selection
FOR x ← a TO b STEP s … END FOR	Counting loop
WHILE cond … END WHILE	Conditional loop
REPEAT … UNTIL cond	Post-test loop
CASE … END CASE	Multi-way selection
BEGIN / END	Block markers (some textbooks)

Reading vs writing pseudocode

The HKEAA may:

1. Show pseudocode and ask for output / a trace table.
2. Ask you to write pseudocode for a given problem.
3. Ask you to convert pseudocode into Python.

For all three you must respect the conventions above.

Worked example · Maximum of three numbers

INPUT a, b, c
max ← a
IF b > max THEN max ← b END IF
IF c > max THEN max ← c END IF
OUTPUT max

Translating to Python (quick reference)

Pseudocode	Python
INPUT x	x = int(input())
OUTPUT x	print(x)
x ← 5	x = 5
IF a = b THEN	if a == b:
IF a >= b THEN … ELSE …	if a >= b: … else: …
FOR i ← 1 TO n	for i in range(1, n+1):
WHILE cond	while cond:

Common student mistakes

• Writing = for assignment in pseudocode (use ←).
• Mixing Python == for comparison (use single =).
• Forgetting END FOR / END IF.
• Adding language-specific constructs like try/except to pseudocode.

Exam-style question

Q (5 marks): Write pseudocode that reads 10 numbers from the user and outputs how many are positive, negative, and zero.

Sample answer:

positives ← 0
negatives ← 0
zeros     ← 0
FOR i ← 1 TO 10
    INPUT n
    IF n > 0 THEN
        positives ← positives + 1
    ELSE IF n < 0 THEN
        negatives ← negatives + 1
    ELSE
        zeros ← zeros + 1
    END IF
END FOR
OUTPUT positives, negatives, zeros

Key takeaways

• HKEAA-style pseudocode: caps keywords, ← for assignment, END FOR/IF.
• Use it to communicate algorithms before coding.

➡️ Next: 2.2 Flowcharts