Pseudocode: OCR Reference Language Conventions

This lesson covers pseudocode and the OCR Exam Reference Language conventions, as required by OCR J277 Section 2.1. Pseudocode is used extensively in the OCR GCSE Computer Science exam, so understanding the OCR reference language is essential.

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What Is Pseudocode?

Pseudocode is a way of writing algorithms that looks like a simplified programming language but is not tied to any specific language. It uses structured, English-like statements to describe the logic of an algorithm.

Pseudocode is:

• Language-independent — It does not follow the syntax of any specific programming language
• Readable — Easier to understand than actual code
• Structured — Uses indentation and keywords to show the logic clearly
• Used in exams — OCR uses its own pseudocode reference language in the exam

OCR Exam Tip: In the exam, pseudocode questions use the OCR Exam Reference Language. You do not need to use perfect syntax, but you should follow the OCR conventions. The reference language guide is available on the OCR website and will be familiar from your practice.

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OCR Pseudocode Conventions

Variables and Assignment

Variables are assigned using =:

name = "Alice"
age = 16
total = 0

Data Types

Data Type	Description	Example
Integer	Whole number	age = 16
Real	Decimal number	price = 9.99
Boolean	True or False	found = true
Character	Single character	grade = 'A'
String	Text (sequence of characters)	name = "Alice"

Arithmetic Operators

Operator	Meaning	Example	Result
+	Addition	3 + 2	5
-	Subtraction	10 - 4	6
*	Multiplication	5 * 3	15
/	Division	10 / 3	3.33...
MOD	Modulus (remainder)	10 MOD 3	1
DIV	Integer division (quotient)	10 DIV 3	3
^	Exponentiation (power)	2 ^ 3	8

OCR Exam Tip: MOD and DIV are commonly tested. MOD gives the remainder (10 MOD 3 = 1), DIV gives the whole number result of division (10 DIV 3 = 3). Learn these well — they appear in many exam questions.

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Input and Output

// Input
name = input("Enter your name: ")

// Output
print("Hello")
print(name)
print("Your score is " + score)

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Selection (IF Statements)

Simple IF:

if score >= 50 then
    print("Pass")
endif

IF...ELSE:

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

IF...ELSEIF...ELSE:

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

SWITCH/CASE:

switch day:
    case "Monday":
        print("Start of the week")
    case "Friday":
        print("End of the week")
    default:
        print("Midweek")
endswitch

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Iteration (Loops)

FOR Loop (count-controlled):

for i = 1 to 10
    print(i)
next i

FOR Loop with STEP:

for i = 0 to 20 step 2
    print(i)
next i

WHILE Loop (condition-controlled — pre-check):

while answer != "quit"
    answer = input("Enter command: ")
endwhile

DO...UNTIL Loop (condition-controlled — post-check):

do
    password = input("Enter password: ")
until password == "secret"

Loop Type	When to Use	Checks Condition
FOR	When you know how many times to repeat	Before each iteration
WHILE	When you do not know how many times — check before executing	Before each iteration (may not execute at all)
DO...UNTIL	When you want to execute at least once	After each iteration (always executes at least once)

OCR Exam Tip: Know when to use each loop type. Use FOR when the number of repetitions is known. Use WHILE when the condition must be checked BEFORE each iteration. Use DO...UNTIL when the loop body must execute AT LEAST ONCE. This distinction is commonly tested.

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Comparison Operators

Operator	Meaning	Example
==	Equal to	if x == 5
!=	Not equal to	if x != 0
<	Less than	if age < 18
<=	Less than or equal to	if score <= 100
>	Greater than	if temp > 30
>=	Greater than or equal to	if marks >= 50

Boolean Operators

Operator	Meaning	Example
AND	Both conditions must be true	if age >= 13 AND age <= 19
OR	At least one condition must be true	if day == "Saturday" OR day == "Sunday"
NOT	Reverses the condition	if NOT found

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String Operations

Operation	Syntax	Example	Result
Length	string.length	"Hello".length	5
Substring	string.substring(start, length)	"Hello".substring(1, 3)	"ell"
Uppercase	string.upper	"hello".upper	"HELLO"
Lowercase	string.lower	"HELLO".lower	"hello"
ASCII	ASC(char)	ASC('A')	65
Character	CHR(code)	CHR(65)	'A'

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Arrays

// Declare an array
array names[5]

// Assign values
names[0] = "Alice"
names[1] = "Bob"
names[2] = "Charlie"

// Access values
print(names[0])  // Outputs: Alice

// Loop through an array
for i = 0 to 4
    print(names[i])
next i

Note: In OCR pseudocode, arrays are zero-indexed (the first element is at index 0).

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Functions and Procedures

Procedure (no return value):

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

// Calling a procedure
greet("Alice")

Function (returns a value):

function calculateArea(length, width)
    area = length * width
    return area
endfunction

// Calling a function
result = calculateArea(5, 3)
print(result)  // Outputs: 15

OCR Exam Tip: Know the difference: a procedure performs an action but does not return a value. A function performs a calculation and returns a value that can be stored in a variable. The exam may ask you to write either one.

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Summary

Pseudocode is a structured, language-independent way of writing algorithms. The OCR Exam Reference Language uses specific conventions for variables, input/output, selection, iteration, arrays, and subprograms. For the OCR J277 exam, you must be able to read, write, and trace through pseudocode. Pay particular attention to MOD/DIV, loop types, and the difference between functions and procedures.

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Worked Example: Validating a Student PIN

A school wants to give each student a 4-digit PIN to log into a library kiosk. The kiosk must accept an attempted PIN, compare it with the stored PIN, and either grant access or lock the account after three wrong attempts.

Design in OCR pseudocode:

storedPIN = "4721"
attempts = 0
locked = false