Cambridge International AS & A-Level 9618 Pseudocode Guide

At A-Level 9618, algorithms frequently group heterogeneous data fields into composite records using the TYPE ... ENDTYPE construct:

// 1. Define the Composite Record Structure
TYPE StudentRecord
    DECLARE StudentID : STRING
    DECLARE Marks : ARRAY[1:5] OF INTEGER
    DECLARE Passed : BOOLEAN
ENDTYPE

// 2. Instantiate and Access Record Variables
DECLARE TopStudent : StudentRecord
TopStudent.StudentID ← "ST-1049"
TopStudent.Marks[1] ← 92
TopStudent.Passed ← TRUE

OUTPUT "Student ID: ", TopStudent.StudentID

Records can also be combined into 1D arrays to represent database tables in memory: DECLARE ClassList : ARRAY[1:30] OF StudentRecord.

Cambridge 9618 requires candidates to implement abstract data types using arrays and pointer index trackers:

• Stack (LIFO - Last In First Out): Implemented with an array and a TopPointer : INTEGER. Push increments the pointer and stores the item; Pop reads the item and decrements the pointer. Must check for Stack Overflow and Stack Underflow.
• Queue (FIFO - First In First Out): Uses HeadPointer and TailPointer. Linear queues require shift operations; circular queues use modulo arithmetic: TailPointer ← (TailPointer MOD MaxQueue) + 1.
• Linked List: Constructed using parallel arrays: DataArray[1:N] and PointerArray[1:N], along with StartPointer and FreeListPointer.

A recursive subroutine is one that calls itself directly or indirectly. On Paper 2, candidates must identify the base case (terminating condition) and trace the activation records on the call stack:

FUNCTION Factorial(n : INTEGER) RETURNS INTEGER
    IF n = 0 THEN
        RETURN 1       // Base Case
    ELSE
        RETURN n * Factorial(n - 1)  // Recursive Step
    ENDIF
ENDFUNCTION

Examiners frequently ask students to draw trace trees or state the return value of deep recursive calls (such as Binary Tree traversals or recursive countdown algorithms).

Cambridge A-Level 9618 introduces formal Object-Oriented syntax to pseudocode. Candidates must follow exact encapsulation and constructor conventions:

CLASS Vehicle
    PRIVATE RegistrationNumber : STRING
    PRIVATE EngineSize : INTEGER

    PUBLIC PROCEDURE NEW(Reg : STRING, Engine : INTEGER)
        RegistrationNumber ← Reg
        EngineSize ← Engine
    ENDPROCEDURE

    PUBLIC FUNCTION GetReg() RETURNS STRING
        RETURN RegistrationNumber
    ENDFUNCTION
ENDCLASS

// Instantiating Class Objects
DECLARE Car1 : Vehicle
Car1 ← NEW Vehicle("AB26-XYZ", 1800)
OUTPUT "Registered car: ", Car1.GetReg()

For inheritance, use CLASS Car INHERITS Vehicle and call the superclass constructor inside the child's NEW routine.

In A-Level 9618, Paper 2 is theory-based (written on paper using Cambridge pseudocode), while Paper 4 is practical (coding in Python 3, Java, or VB on an exam computer). The table below highlights how 9618 topics translate to Paper 4 Python: