Pseudocode basics (Cambridge International AS Computer Science)

Exam board Cambridge International · ASUpdated 2026-10-01

Variables & Constants

What is a variable?

A variable is an identifier that can change in the lifetime of a program
Identifiers should be:
- In mixed case (Pascal case)
- Can only contain letters (A-Z, a-z), digits (0-9) and the underscore character (_)
- Start with a capital letter and not a digit
A variable can be associated a datatype when it is declared
When a variable is declared, memory is allocated based on the data type indicated

Pseudocode
`DECLARE <identifier> : <datatype>`

To declare a variable, use the DECLARE keyword followed by the name and data type:
You can then assign a value using the assignment operator ← :

What is a constant?

A constant is an identifier set once in the lifetime of a program
Constants are generally named in all uppercase characters
Constants aid the readability and maintainability

Pseudocode
`CONSTANT <identifier> = <value>`

To declare a constant, use the CONSTANT keyword:
Constants are not reassigned during execution – they are fixed values used throughout the algorithm

Example

You are writing a program to calculate the area of a circle using the formula:

Area ← π × radius²

π is a constant (it never changes)
radius and area are variables (they change depending on the input)

Variables and constants in different languages

Feature	Python	VB.NET	Java
Declare variable	Just assign it (no keyword needed)	`Dim radius As Double`	`double radius;`
Assign variable	`radius = 5`	`radius = 5`	`radius = 5;`
Declare constant	Convention: use UPPERCASE (`PI = 3.14`) (not enforced)	`Const Pi As Double = 3.14159`	`final double PI = 3.14159;`
Reassign constant?	Yes (not truly constant unless enforced)	Cannot change once set	Cannot change once set
Use in calc.	`area = PI * radius * radius`	`area = Pi * radius * radius`	`area = PI * radius * radius;`

Arithmetic & logical operators

Arithmetic operators

Arithmetic operators are used to perform basic maths operations in a program
These include adding, subtracting, multiplying and dividing values

Common arithmetic operators

Operator	Purpose	Example	Result
`+`	Addition	`5 + 3`	`8`
`&`	Concatenation	`"John" & " " & "Doe"`	`"John Doe"`
`-`	Subtraction	`10 - 4`	`6`
`*`	Multiplication	`3 * 5`	`15`
`/`	Division	`10 / 2`	`5`
`^`	Exponentiation (power of)	`3 ^ 3`	`27`
`MOD`	Modulus (remainder after division)	`10 MOD 3`	`1`

Operator precedence (BODMAS / BIDMAS)

Arithmetic operators follow operator precedence
Multiplication and division happen before addition and subtraction unless brackets are used

Relational and logic operators

Relational operators (also called comparison operators) are used to compare two values
They return either TRUE or FALSE and are commonly used in conditions and loops
The logic operators are AND, OR and NOT; they combine or reverse BOOLEAN values, e.g. X < Y AND Y < 20

Common relational operators

Operator	Purpose	Example	Result
`=`	Equal to	`5 = 6`	`FALSE`
`<>`	Not equal to	`5 <> 7`	`TRUE`
`>`	Greater than	`5 > 10`	`FALSE`
`<`	Less than	`5 < 10`	`TRUE`
`>=`	Greater than or equal to	`5 >= 10`	`FALSE`
`<=`	Less than or equal to	`5 <= 10`	`TRUE`

Example code

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Pseudocode

DECLARE <identifier> : <datatype>

Pseudocode

CONSTANT <identifier> = <value>

Feature

Python

VB.NET

Java

Declare variable

Just assign it (no keyword needed)

Dim radius As Double

double radius;

Assign variable

radius = 5

radius = 5;

Declare constant

Convention: use UPPERCASE (PI = 3.14) (not enforced)

Const Pi As Double = 3.14159

final double PI = 3.14159;

Reassign constant?

Yes (not truly constant unless enforced)

Cannot change once set

Use in calc.

area = PI * radius * radius

area = Pi * radius * radius

area = PI * radius * radius;

Operator

Purpose

Example

Result

+

Addition

5 + 3

8

&

Concatenation

"John" & " " & "Doe"

"John Doe"

-

Subtraction

10 - 4

6

*

Multiplication

3 * 5

15

/

Division

10 / 2

5

^

Exponentiation (power of)

3 ^ 3

27

MOD

Modulus (remainder after division)

10 MOD 3

1

Operator

Purpose

Example

Result

=

Equal to

5 = 6

FALSE

<>

Not equal to

5 <> 7

TRUE

>

Greater than

5 > 10

FALSE

<

Less than

5 < 10

TRUE

>=

Greater than or equal to

5 >= 10

FALSE

<=

Less than or equal to

5 <= 10

TRUE