What does a variable declaration do?

It introduces an identifier and states its data type, so that memory is reserved for it and the translator knows how to interpret and check its use. In some languages a variable is declared explicitly before use; in others it is created implicitly the first time it is assigned to.

What does a constant declaration do?

It gives a name to a fixed value that is set when the program is written and cannot be changed while the program runs, for example CONST VAT = 0.2. Any later attempt to assign to it is rejected by the translator.

Explain what an assignment statement does.

It stores a value in a variable. The expression on the right-hand side is evaluated first and the resulting value is copied into the variable named on the left, overwriting whatever it held before. This is why count = count + 1 is perfectly sensible as an assignment even though it is nonsense as an equation.

What does an iteration statement do?

It causes a block of statements to be executed more than once, either a set number of times or until a condition is met, without that block having to be written out repeatedly.

What does a selection statement do?

It chooses between alternative blocks of statements according to whether a condition is True or False, using structures such as IF, IF...ELSE, or a CASE/SWITCH statement that selects one branch from many according to the value of an expression.

AQA A-Level Computer Science 7517

Fundamentals of Programming

Topic overview Data types Programming concepts and program structure Arithmetic operations Relational Operations, Constants and Variables Boolean operations String-handling operations Random numbers and exception handling Subroutines, parameters and return values Variable scope and stack frames Recursive techniques Programming paradigms and the procedural approach Classes, Objects, Inheritance and Polymorphism Aggregation, Composition, Class Diagrams and Design Principles

Fundamentals of Data Structures

Topic overview Data Structures and Abstract Data Types Static and Dynamic Data Structures Queues and Linear Queues Circular and Priority Queues Stacks Graphs Trees Hash tables Dictionaries Vectors and Their Notation Vector Arithmetic and Geometry

Fundamentals of Algorithms

Topic overview Graph traversal Tree traversal Reverse Polish notation Searching algorithms Sorting algorithms Optimisation algorithms

Theory of Computation

Topic overview Logic Problems and Algorithm Constructs Pseudo-Code, Hand-Tracing and Program Correctness Representational Abstraction, Generalisation and Information Hiding Procedural and Functional Abstraction Data Abstraction and Problem Reduction Decomposition and Composition Automation and Finite State Machines Sets and Set Notation Subsets and Set Operations Regular expressions and regular languages Backus-Naur Form and syntax diagrams Comparing Algorithms and Functions Order of complexity and Big-O notation Limits of computation, tractability and heuristics Computable problems and the Halting problem Turing machines

Fundamentals of Data Representation

Topic overview Number systems and the sets of numbers Number bases: decimal, binary and hexadecimal Bits, bytes and units of information Unsigned binary and binary arithmetic Signed binary using two's complement Fixed point and floating point representation Normalisation of floating point numbers Rounding errors, accuracy, range and precision Character coding systems Error checking and correction Bit patterns, analogue and digital Bitmapped graphics Vector graphics Digital representation of sound MIDI and Data Compression Encryption

Fundamentals of Computer Systems

Topic overview Hardware, Software and Its Classification System Software and the Operating System Translators and the Role of the Operating System Classification of programming languages Types of program translator Logic Gates and Their Truth Tables Logic Circuits and D-Type Flip-Flops Half-Adders and Full Adders Boolean algebra

Fundamentals of Computer Organisation and Architecture

Topic overview Internal components, buses and von Neumann and Harvard architectures The Stored Program Concept and the Processor The Fetch-Execute cycle The processor instruction set Addressing modes Machine-Code Operations Shifts, Halting and Assembly Language Programs Interrupts Factors affecting processor performance Input and output devices Secondary storage devices

Fundamentals of Communication and Networking

Topic overview Communication methods Communication basics Network Topology and Types of Networking Wireless networking The Internet and Packet Switching Routing, URLs and Domain Names Firewalls, Worms, Trojans and Viruses Encryption, Digital Signatures and Certificates TCP/IP Standard application layer protocols IP Address Structure and Subnet Masking IP Standards and Public and Private Addresses DHCP and Network Address Translation Client server model Thin- versus thick-client computing

Consequences of Uses of Computing

Topic overview The Four Kinds of Issue in Computing Legislation, Ethical Dilemmas and Case Studies

Systematic Approach to Problem Solving

Topic overview Analysis, Design and Implementation Testing and Evaluation

Fundamentals of Databases

Topic overview Conceptual data models and entity relationship modelling Relational databases Database design and normalisation techniques Structured Query Language (SQL)Client server databases

Big Data

Topic overview Volume, Velocity and Variety Why Big Data Resists Analysis Distributed Processing and Functional Programming Fact-Based Models and Graph Schemas

Fundamentals of Functional Programming

Topic overview Function Types, First-Class Objects and Function Application Partial Function Application and Composition Writing functional programs Lists in functional programming

Fundamentals of Programming

Programming concepts and program structure

3 things to know
Paper 1

Overview

Recall questions on the three combining principles of imperative languages, and on declaration, assignment, selection, iteration and subroutines as statement types.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

What are the three combining principles on which all imperative programming languages are built?

Numbers

Define indefinite iteration.

Key term

You need to keep asking the user for a password until the correct one is entered. Which position of the condition suits this, and why?

Questions from this subtopic

Each one with the model answer underneath.

1
What are the three combining principles on which all imperative programming languages are built?
Model answer
Sequence, in which statements are carried out one after another in the order written; iteration or repetition, in which a block of statements is carried out repeatedly; and selection or choice, in which a block is carried out only when a condition is met. Every imperative program is built by combining these three.
2
What does a variable declaration do?
Model answer
It introduces an identifier and states its data type, so that memory is reserved for it and the translator knows how to interpret and check its use. In some languages a variable is declared explicitly before use; in others it is created implicitly the first time it is assigned to.
3
What does a constant declaration do?
Model answer
It gives a name to a fixed value that is set when the program is written and cannot be changed while the program runs, for example CONST VAT = 0.2. Any later attempt to assign to it is rejected by the translator.
4
Explain what an assignment statement does.
Model answer
It stores a value in a variable. The expression on the right-hand side is evaluated first and the resulting value is copied into the variable named on the left, overwriting whatever it held before. This is why count = count + 1 is perfectly sensible as an assignment even though it is nonsense as an equation.
5
What does an iteration statement do?
Model answer
It causes a block of statements to be executed more than once, either a set number of times or until a condition is met, without that block having to be written out repeatedly.
6
What does a selection statement do?
Model answer
It chooses between alternative blocks of statements according to whether a condition is True or False, using structures such as IF, IF...ELSE, or a CASE/SWITCH statement that selects one branch from many according to the value of an expression.

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