The pseudocode shown represents a queue Abstract Data Type (ADT) with procedures for initialisation and to add new items. It is incomplete.

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

1. [2] One mark for every two correct identifiers (Max 2) Identifier Data type Description Queue STRING An array to store the contents of the queue. RearPointer INTEGER Points to the last term of the queue. Length INTEGER Indicates the number of items in the queue. FrontPointer INTEGER Points to the first term of the queue.
2. [5] One mark for each correctly completed line (Max 5) CONSTANT MaxLength = 50 DECLARE FrontPointer : INTEGER DECLARE RearPointer : INTEGER DECLARE Length : INTEGER DECLARE Queue : ARRAY[0:MaxLength - 1] OF STRING // Initialisation of queue PROCEDURE Initialise FrontPointer ← -1 RearPointer ← -1 Length ← 0 ENDPROCEDURE // Adding a new item to the queue PROCEDURE Enqueue(NewItem : STRING) IF Length < MaxLength THEN // IF Length <= MaxLength - 1 THEN RearPointer ← RearPointer + 1 IF RearPointer > MaxLength - 1 THEN RearPointer ← 0 ENDIF Queue[RearPointer] ← NewItem Length ← Length + 1 ENDIF ENDPROCEDURE
3. [3] One mark per mark point (Max 3) • Print jobs are expected to be actioned by the printer in the order they are received • ... because the printer queue is a queue, the first job to be sent to the printer would be the first job printed. • If the printer queue was on a stack, the first job the printer received would not be printed until all the other jobs have been printed.