Pseudocode & Exam Reference Language (ERL) — Complete GCSE & A Level Guide

Pseudocode is one of the most misunderstood parts of GCSE and A Level Computer Science exams. Students who know Python well often lose marks because they write Python instead of pseudocode — and the examiner can’t give full credit.

This guide covers both AQA pseudocode and OCR’s Exam Reference Language (ERL), the two most common formats used in UK Computer Science exams.

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Why pseudocode matters in exams

Exam boards use pseudocode (or ERL) rather than a specific programming language because:

1. Exam fairness — students may be using Python, C#, VB, or other languages
2. Clarity — pseudocode strips away language-specific syntax so the algorithm logic is clear
3. Flexibility — pseudocode can express ideas that are awkward in specific languages

In AQA Paper 1 and OCR J277 Component 02, you will be asked to:

• Read and trace pseudocode
• Write pseudocode solutions to problems
• Identify errors in pseudocode

You will lose marks if you write Python when the question asks for pseudocode.

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AQA Pseudocode

Variables and assignment

name ← 'Alice'
age ← 17
score ← 0.0
isValid ← TRUE

The assignment arrow (←) replaces =. In an AQA exam you may write either, but ← is the official format.

Input and output

name ← USERINPUT
OUTPUT 'Hello, ', name

USERINPUT reads from the keyboard. OUTPUT displays to the screen. No brackets or parentheses needed.

Arithmetic and string operations

total ← price * quantity
remainder ← total MOD 3        # modulus (remainder)
quotient ← total DIV 3         # integer division
result ← total ^ 2             # power / exponent

# String operations
length ← LEN(name)             # length of string
upper ← name.upper             # uppercase
lower ← name.lower             # lowercase
sub ← name.substring(0, 3)     # characters 0, 1, 2
combined ← first + ' ' + last  # concatenation

Selection (IF statements)

IF score >= 70 THEN
  OUTPUT 'Distinction'
ELSEIF score >= 50 THEN
  OUTPUT 'Pass'
ELSE
  OUTPUT 'Fail'
ENDIF

Every IF block must end with ENDIF. The ELSEIF keyword (one word) is used for additional conditions.

Switch / case

SWITCH day:
  CASE 'Mon':
    OUTPUT 'Monday'
  CASE 'Tue':
    OUTPUT 'Tuesday'
  DEFAULT:
    OUTPUT 'Unknown day'
ENDSWITCH

Iteration: FOR loops

FOR i ← 0 TO 9
  OUTPUT i
NEXT i

AQA FOR loops are inclusive on both ends. FOR i ← 0 TO 9 iterates 10 times (0, 1, 2, …, 9).

# Counting down
FOR i ← 10 TO 1 STEP -1
  OUTPUT i
NEXT i

Iteration: WHILE loops

count ← 0
WHILE count < 10 DO
  OUTPUT count
  count ← count + 1
ENDWHILE

Iteration: REPEAT…UNTIL (do-while)

REPEAT
  answer ← USERINPUT
UNTIL answer = 'quit'

REPEAT…UNTIL always executes at least once. The condition is checked after the body.

Arrays

# Creating arrays
scores ← [85, 72, 91, 64, 78]
names ← ['Alice', 'Bob', 'Charlie']

# 2D array (3 rows, 4 columns)
grid ← [[0,0,0,0], [0,0,0,0], [0,0,0,0]]

# Accessing elements (0-indexed)
first ← scores[0]       # 85
grid[1][2] ← 7          # set row 1, col 2 to 7

Subroutines (procedures and functions)

# Procedure (no return value)
SUBROUTINE greet(name)
  OUTPUT 'Hello, ', name
ENDSUBROUTINE

# Function (returns a value)
SUBROUTINE square(n)
  RETURN n * n
ENDSUBROUTINE

# Calling subroutines
greet('Alice')
result ← square(5)

File handling

myFile ← OPENREAD('data.txt')
WHILE NOT myFile.endOfFile()
  line ← myFile.readLine()
  OUTPUT line
ENDWHILE
myFile.close()

# Writing to a file
myFile ← OPENWRITE('output.txt')
myFile.writeLine('Hello')
myFile.close()

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OCR Exam Reference Language (ERL)

OCR uses ERL for J277 (GCSE) and H446 (A Level). It is similar to AQA pseudocode but with some key differences.

Variables and assignment

name = "Alice"          // Uses = not ←
age = 17
score = 0.0
isValid = true           // lowercase boolean literals

ERL uses = for assignment and == for comparison (unlike AQA which uses = for both).

Input and output

name = input("Enter your name: ")
print("Hello, " + name)

ERL uses input() and print() — almost identical to Python.

Arithmetic

remainder = total % 3    // modulus (ERL uses % not MOD)
quotient = total // 3    // integer division (ERL uses //)
result = total ** 2      // power (ERL uses **)

Selection

if score >= 70 then
    print("Distinction")
elseif score >= 50 then
    print("Pass")
else
    print("Fail")
endif

ERL uses lowercase keywords (if, then, else, endif) and lowercase print.

Iteration: FOR loops (ERL)

for i = 0 to 9
    print(i)
next i

ERL’s FOR loop is also inclusive. Note: = 0 to 9 not ← 0 TO 9.

WHILE loops (ERL)

count = 0
while count < 10 do
    print(count)
    count = count + 1
endwhile

Procedures and functions (ERL)

procedure greet(name)
    print("Hello, " + name)
endprocedure

function square(n)
    return n * n
endfunction

greet("Alice")
result = square(5)

Arrays (ERL)

scores = [85, 72, 91, 64, 78]
first = scores[0]

# 2D array
grid = [[0,0,0,0], [0,0,0,0], [0,0,0,0]]
grid[1][2] = 7

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Side-by-side comparison

Feature	AQA Pseudocode	OCR ERL
Assignment	x ← 5	x = 5
Comparison	x = 5	x == 5
Output	OUTPUT x	print(x)
Input	x ← USERINPUT	x = input(...)
FOR loop	FOR i ← 0 TO 9	for i = 0 to 9
WHILE	WHILE ... DO	while ... do
MOD	x MOD y	x % y
Integer div	x DIV y	x // y
Power	x ^ y	x ** y
Function	SUBROUTINE	function
Boolean	TRUE/FALSE	true/false

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Common exam question patterns

Pattern 1: Trace a program

You’re given pseudocode and must complete a trace table showing the value of variables at each step.

Tip: Work through one line at a time. Don’t skip ahead. Always show the assignment before the output.

Pattern 2: Identify and fix an error

You’re given code with a bug and must identify whether it’s a:

• Syntax error — invalid code that won’t run (e.g., wrong keyword)
• Logic error — code runs but gives wrong output (e.g., > instead of >=)
• Runtime error — code crashes during execution (e.g., dividing by zero)

Pattern 3: Write pseudocode for an algorithm

These are the most heavily marked questions (6–12 marks). Read the question very carefully:

• Underline what inputs are needed
• Underline what outputs are required
• Plan your algorithm in plain English first
• Then translate to pseudocode

Common algorithms you might need to write:

• Linear search
• Bubble sort
• Input validation (WHILE loop with range check)
• Totalling values in an array
• Finding the maximum/minimum value
• Counting how many values match a condition

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Exam technique for pseudocode questions

1. Use the correct format — AQA questions expect AQA pseudocode. OCR questions expect ERL. Don’t mix them up.
2. Show your structure clearly — indent consistently, use ENDFOR/ENDIF/ENDWHILE
3. Name variables clearly — totalScore is better than x
4. Check your loop bounds — is it 0 TO 9 or 1 TO 10? (They’re not the same!)
5. Don’t over-engineer — write the simplest correct solution, not the cleverest one

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Practice: converting Python to pseudocode

A common question style gives you Python and asks you to write the equivalent pseudocode:

Python:

def factorial(n):
    result = 1
    for i in range(1, n + 1):
        result = result * i
    return result

AQA Pseudocode equivalent:

SUBROUTINE factorial(n)
  result ← 1
  FOR i ← 1 TO n
    result ← result * i
  NEXT i
  RETURN result
ENDSUBROUTINE

OCR ERL equivalent:

function factorial(n)
    result = 1
    for i = 1 to n
        result = result * i
    next i
    return result
endfunction

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Pseudocode mastery comes from practice. The best approach is to take any algorithm you’ve written in Python and rewrite it in pseudocode — you’ll quickly spot where the differences matter.

For practice questions on pseudocode and algorithms, use the question bank. For one-to-one help with programming and exam technique, book a session.