Paper 3 May/June 2021

Describe the purpose of a user-defined data type.

• To create a new data type (from existing data types)

• To allow data types not available in a programming language to be constructed // To extend the flexibility of the programming language

Explain how an interpreter executes a program without producing a complete translated version.

• An interpreter examines source code one statement at a time

• Check each statement for errors

• If no error is found the statement is executed

• If an error is found this is reported and the interpreter halts

Explain why Reverse Polish Notation (RPN) is used to evaluate expressions.

• Reverse Polish Notation provides an unambiguous method of representing an expression

• Reading from left to right

• Without the need to use brackets

• With no need for rules of precedence / BODMAS

Identify a data structure used to evaluate an expression in RPN, with a reason.
A:

Structure: stack
Reason: The operands are popped from the stack in the reverse order to how they were pushed

Explain the use of graphs to aid Artificial Intelligence (AI).

• Artificial Neural Networks can be represented using graphs

• Graphs provide structures for relationships

• AI problems can be defined as finding a path in a graph

• Used in machine learning

Give two benefits and two drawbacks of packet switching.

Benefits:

• Accuracy – Ensures accurate delivery of the message

• Completeness – Missing packets can be easily detected and a re-send request sent so the message arrives complete

• Resilience – if a network changes the router can detect this and send the data another way to ensure it arrives

Drawbacks:

• Time delays to correct errors // Network problems may introduce errors in packets

• Requires complex protocols for delivery

• Unsuitable for real time transmission applications

State two factors that may affect the performance of a sorting algorithm.

• The initial order of the data

• The number of data items to be sorted

• The efficiency of the sorting algorithm

Describe what is meant by an imperative (procedural) programming language

• Imperative languages use variables

• Which are changed using (assignment) statements

• They rely on a method of repetition

Describe what is meant by a declarative programming language.

• Instructs a program on what needs to be done instead of how to do it

• Using facts and rules

• Using queries to satisfy goals

• Can be logical or functional

Identify the programming paradigms for each of the following program code examples.

• male(john). →

• FOR Counter = 1 TO 20 →

• LDD Counter … →

• public class Vehicle … →

• male(john). → Declarative

• FOR Counter = 1 TO 20 → Procedural / imperative

• LDD Counter … → Low-level / assembly

• public class Vehicle … → Object oriented / (OOP)