Pseudocode Hub - Master CIE IGCSE & AS Level Pseudocode

3.1 What is a Variable?

A variable is a named storage location in a computer's memory that holds a value which can change while a program runs. Think of it as a labelled box — the label is the variable's name, and the contents are the value currently stored inside.

Key idea: The name of a variable stays the same, but the value inside it can change as the program runs. That's why it's called a variable!

Why do we use variables?

To store user input or calculated results for later use
To reuse values without re-typing them every time
To make code readable by giving meaningful names to data
To allow a program to react to changing data at run time

Here's a tiny example that stores and uses a value:

DECLARE Age : INTEGER
Age <- 15
OUTPUT "You are " + Age + " years old."

Knowledge Check 1

What is a Variable?

3.2 Declaring Variables

Before you can use a variable, you have to declare it. In CIE pseudocode this is done with the DECLARE keyword followed by the variable's name, a colon, and its data type.

Syntax

DECLARE <Name> : <Type>

Examples

DECLARE Score : INTEGER
DECLARE Price : REAL
DECLARE UserName : STRING
DECLARE IsReady : BOOLEAN

After a variable is declared, you can give it a value using the assignment operator <-:

DECLARE Score : INTEGER
Score <- 100
OUTPUT Score

Remember: Declaring a variable only creates the "box". It does not put anything inside — you must assign a value before using it.

Knowledge Check 2

Declaring & Assigning Variables

3.3 Data Types

A data type tells the computer what kind of value a variable will hold. Choosing the right type keeps your program correct and efficient. These are the data types used in CIE pseudocode:

Type	Stores	Example
INTEGER	Whole numbers	42, -7, 0
REAL	Numbers with decimals	3.14, -0.5
STRING	Text (in quotes)	"Hello", "Bob"
CHAR	A single character	'A', '7'
BOOLEAN	True or False only	TRUE, FALSE
ARRAY	A collection of values	[1, 2, 3, 4]

DECLARE Age : INTEGER
DECLARE Temperature : REAL
DECLARE FirstName : STRING
DECLARE Initial : CHAR
DECLARE IsLoggedIn : BOOLEAN

Tip: Picking the right type matters! Storing an age as a STRING would stop you doing maths with it. Storing a price as an INTEGER would lose the decimal part.

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Data Types

3.4 Variable Naming Rules

Good variable names make your code easy to read and understand. CIE pseudocode (like most languages) has rules about what is and isn't allowed as a variable name.

The Rules

Must start with a letter (A–Z, a–z)

Can contain letters, digits and underscores _

Cannot contain spaces

Cannot be a reserved keyword (e.g. DECLARE, IF, OUTPUT)

Should be descriptive and meaningful

Are case-sensitive — Score and score are different

Valid vs Invalid Examples

Valid

Total_Score
Age
StudentName
Price1

Invalid

2ndPlace (starts with digit)
Student Name (has space)
OUTPUT (keyword)
Total-Score (hyphen not allowed)

Knowledge Check 4

Variable Naming Rules

3.5 Constants

A constant is like a variable, but its value is set once when the program is written and can never change while the program runs. Use constants for values that should stay the same — like tax rates, conversion factors, or settings.

Syntax

CONSTANT <Name> <- <Value>

Examples

CONSTANT PI <- 3.14159
CONSTANT VAT_RATE <- 0.20
CONSTANT MAX_USERS <- 100

OUTPUT "Circumference: " + 2 * PI * Radius

Why use constants? If you ever need to change a value (say VAT goes from 20% to 22%), you only need to change it in one place. The rest of your code automatically uses the new value.

Variable vs Constant

Feature	Variable	Constant
Keyword	DECLARE	CONSTANT
Type needed?	Yes (e.g. INTEGER)	No — inferred from value
Value can change?	Yes, any time	No — fixed forever
Example use	User input, counters	PI, tax rate, MAX_SIZE

Knowledge Check 5

Constants

3.6 Key Points Summary

Let's recap the most important ideas from this topic before you tackle the Question Bank.

A variable is a named storage location whose value can change.

Use the DECLARE keyword to create a variable: DECLARE Name : Type.

The assignment operator is <- (an arrow, not =).

Common types: INTEGER, REAL, STRING, CHAR, BOOLEAN, ARRAY.

Variable names must start with a letter, contain no spaces, and not be keywords.

Names are case-sensitive: Score and score are different.

Constants use CONSTANT Name <- Value and never change.

Always pick the most appropriate data type for the value you are storing.

Exam tip: In CIE exams, always write pseudocode with UPPERCASE keywords (DECLARE, OUTPUT, IF...) and use the <- arrow for assignment. Examiners deduct marks for using = instead of <-.

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