AQA 7517 · Paper 1 · 4.1.1a

Variables, Constants
& Data Types

AQA A-Level Computer Science · Section 4.1 Fundamentals of Programming

WHAT YOU'LL LEARN

Variable & constant declaration · AQA data types · Type casting

EXAM PAPER

Paper 1: On-Screen Exam · 2 hours 30 minutes

Learning Objectives

By the end of this lesson…

Understand the difference between a variable and a constant

Know all AQA 7517 primitive data types and their uses

Apply type casting to convert between data types

Write correct variable declarations using AQA pseudocode

Answer AQA exam questions on data types with confidence

Variables

What is a Variable?

DEFINITION

A named memory location whose value can change during program execution.

AQA PSEUDOCODE

score ← 0

name ← "Alice"

score ← score + 10

PYTHON EQUIVALENT

score = 0

name = "Alice"

score = score + 10

Variables must have meaningful names — no spaces, case-sensitive in most languages. Use camelCase or snake_case.

Constants

What is a Constant?

DEFINITION

A named memory location whose value is set once and cannot change during program execution.

AQA PSEUDOCODE

CONSTANT PI ← 3.14159

CONSTANT MAX_SIZE ← 100

CONSTANT VAT_RATE ← 0.20

WHY USE CONSTANTS?

Prevents accidental modification

Makes code more readable

Change in one place updates everywhere

Data Types

AQA 7517 Primitive Data Types

Data Type	Description	Example	AQA Keyword
Integer	Whole number (positive or negative)	42, -7, 0	INTEGER
Real	Number with decimal point	3.14, -0.5	REAL
Boolean	True or False only	True, False	BOOLEAN
Character	Single character	'A', '5', '!'	CHARACTER
String	Sequence of characters	"Hello World"	STRING

⚠️ AQA uses REAL not "float" — use AQA terminology in exams. Characters are written in single quotes, strings in double quotes.

Type Casting

Converting Between Data Types

Type casting converts a value from one data type to another.

Function	Converts to	AQA Pseudocode	Python
INT(x)	Integer	INT("42") → 42	int("42")
REAL(x)	Real	REAL(5) → 5.0	float(5)
STR(x)	String	STR(42) → "42"	str(42)
BOOL(x)	Boolean	BOOL(1) → True	bool(1)

Common use: reading user input returns a STRING — you must cast to INTEGER before doing arithmetic: age ← INT(USERINPUT)

AQA Pseudocode

Declaring Variables & Constants

VARIABLE EXAMPLES

studentName ← "Bob"

age ← 16

average ← 73.5

passed ← True

grade ← 'A'

CONSTANT EXAMPLES

CONSTANT PASS_MARK ← 40

CONSTANT PI ← 3.14159

CONSTANT SCHOOL_NAME ← "CSZone Academy"

AQA uses ← for assignment. Python uses =. Both are valid in answers — just be consistent.

Watch Out!

Common Exam Mistakes

❌ MISTAKE 1: Wrong terminology

AQA says REAL, not float. AQA says CHARACTER, not char. Use AQA terms to get the mark.

❌ MISTAKE 2: Confusing variable and constant

A constant cannot be changed after initial assignment. PI = 3.14 should always be a CONSTANT, not a variable.

❌ MISTAKE 3: Forgetting type casting on input

USERINPUT always returns a STRING. Write age ← INT(USERINPUT) before arithmetic, not just age ← USERINPUT.

AQA Exam Style

Practice Question

AQA 7517 — Paper 1 Style Question

A program stores a student's name, their exam score (which can include decimal values), and whether they have passed. Identify the most appropriate data type for each of these three values and justify your choices.

[6 marks]

1 mark

Name → String — because it is a sequence of characters

2 marks

Exam score → Real — because it may include a decimal part (e.g. 73.5)

2 marks

Passed → Boolean — because it can only be True or False

1 mark

Each justification linked clearly to the definition of the data type

Summary

Key Terms to Remember

VARIABLE

Named memory location — value can change. Declared with name ← value

CONSTANT

Named memory location — value cannot change. Declared with CONSTANT name ← value

DATA TYPES

INTEGER · REAL · BOOLEAN · CHARACTER · STRING

TYPE CASTING: INT() · REAL() · STR() · BOOL()

Always cast USERINPUT to the correct type before use in calculations

🎉 Lesson complete — move to the quiz to test yourself!