2.2a Variables, Constants & Data Types — Edexcel 1CP2

Variables

A variable is a named storage location in memory whose value can change during the execution of a program. Variables hold data that a program needs to process.

Each variable has a name (identifier), a data type, and a value
The value can be read or updated at any point in the program
Example: score = 0 — 'score' is the identifier, 0 is the value

Constants

A constant is a named value that is set once and cannot be changed during program execution.

Used for values that should never change (e.g., Pi = 3.14159, VAT = 0.20)
Makes code clearer and prevents accidental modification
Example: PI = 3.14159 — this value stays fixed throughout the program

Feature	Variable	Constant
Value can change	✓ Yes	✗ No
Set at runtime	✓ Yes	Set at program start
Prevents modification	✗	✓ Yes
Example use	Player score	Pi, VAT rate

Data Types

Every variable or constant has a data type which determines what kind of data it can store and how much memory it uses.

Data type	Description	Example
Integer	Whole numbers (positive, negative, zero)	42, −7, 0
Real / Float	Numbers with a decimal point	3.14, −0.5
Boolean	True or False only	True, False
Character	A single character	'A', '5', '!'
String	A sequence of characters (text)	"Hello", "CSZone"

Why data types matter

Determines valid operations (you can add integers; you can concatenate strings)
Affects memory allocation
Prevents errors — storing a string where a number is expected causes a type error

Casting (Type Conversion)

Sometimes you need to convert between data types — called casting:

int("42") converts the string "42" to integer 42
str(42) converts integer 42 to string "42"
float("3.14") converts string to real number

Exam tip: Edexcel 1CP2 expects you to identify correct data types for given scenarios, state the difference between variables and constants, and explain why appropriate data types should be used. Remember: integers for counting, reals for measurements, Booleans for conditions.

⚠️ Common Mistakes

Confusing character (single char) with string (sequence of chars)
Saying constants "save memory" — they don't; the benefit is clarity and preventing errors
Using integer for data that can have decimal places (e.g., prices should be real/float)
Forgetting that Boolean only has two values: True or False

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Worksheet — 2.2a Variables, Constants & Data Types

8 Edexcel-style questions · instantly marked

Q1State the difference between a variable and a constant.[2]

✅ Mark scheme

A variable is a named storage location whose value can change during program execution [1]; a constant is a named value that is set once and cannot be changed during execution [1].

Q2Identify the most appropriate data type for each: (a) a person's age, (b) their name, (c) whether they are a member.[3]

✅ Mark scheme

(a) Integer [1]; (b) String [1]; (c) Boolean [1].

Q3Give one reason why constants are used instead of variables in programs.[1]

✅ Mark scheme

Any one: to prevent accidental modification of a fixed value [1]; to improve code readability (a meaningful name is more clear than a magic number) [1].

Q4What is the difference between an integer and a real (float) data type?[2]

✅ Mark scheme

An integer stores whole numbers only (no decimal point) [1]; a real/float stores numbers with decimal places [1].

Q5What is a Boolean data type? Give one example of when it would be used.[2]

✅ Mark scheme

A Boolean can only hold the value True or False [1]; e.g., to store whether a user is logged in (True/False) or whether a game is over [1].

Q6Explain what 'casting' means in programming and give one example.[2]

✅ Mark scheme

Casting is converting a value from one data type to another [1]; e.g., converting a string "42" to integer 42 using int("42") [1].

Q7What is the difference between a character and a string data type?[2]

✅ Mark scheme

A character stores a single symbol/letter/digit [1]; a string stores a sequence of characters (text of any length) [1].

Q8A programmer stores a product price as an integer. Identify the problem and suggest a better data type.[2]

✅ Mark scheme

Integer cannot store decimal places, so prices like £9.99 would be truncated/lost [1]; real/float should be used instead [1].

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Variables

Constants

Data Types

Why data types matter

Casting (Type Conversion)

Worksheet — 2.2a Variables, Constants & Data Types

Mini Test — Variables, Constants & Data Types

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