A stack is to be set up using the information in the table. [Table with Identifier: BasePointer, TopPointer, Stack; Data type: INTEGER, INTEGER, REAL; Description: points to the bottom of the stack, points to the top of the stack, 1D array to implement the stack] A constant, with identifier Capacity, limits the size of the stack to 25 items.

Mark scheme

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

1. [1] One mark per mark point (Max 3) MP1 Correct constant declaration
2. [1] MP2 Two correct variable declarations
3. [1] MP3 Correct array declaration
4. [1] Example answer: CONSTANT Capacity = 25 DECLARE BasePointer : INTEGER DECLARE TopPointer : INTEGER DECLARE Stack : ARRAY[1:25] OF REAL
5. [1] One mark for each correctly completed line (Max 5)
6. [1] One mark per mark point (Max 2) MP1 A queue is a first in first out / FIFO data structure and a stack is a first in last out / FILO / LIFO data structure // Data is removed from a queue in the order it is received and removed from a stack in the reverse order to which it is received
7. [1] MP2 Both ADTs can vary in size / are of indeterminate length
8. [1] MP3 Data is popped and pushed (onto/from a stack) at the same end but it is enqueued and dequeued (to/from a queue) at different/opposite ends // a queue has two accessible ends and a stack has only one
9. [1] MP4 A stack has only one moveable pointer whereas a queue has two.