Variables, Constants
& Operators

Assignment · Constants · Arithmetic · Input & Output

CSZoneAQA GCSE Computer Science 8525

Learning Objectives

By the end of this lesson you will be able to...

Explain the difference between a variable and a constant

Write AQA pseudocode using assignment (←), INPUT and OUTPUT

Use arithmetic operators (+, -, *, /, DIV, MOD) correctly

Choose appropriate names for variables and constants

Variables vs Constants

Storing Data in Programs

VARIABLE

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

score ← 0
score ← score + 10
name ← USERINPUT

CONSTANT

A named value that is fixed throughout the program — it cannot change once set.

CONST MAX_SCORE ← 100
CONST PI ← 3.14159
CONST PASS_MARK ← 50

Why constants?Constants make code easier to read and update — change the constant once, it updates everywhere.

AQA Pseudocode — Input & Output

Getting and Displaying Data

READING INPUT

name ← USERINPUT
age ← INT(USERINPUT)
score ← REAL(USERINPUT)

USERINPUT always returns a String — cast when needed!

DISPLAYING OUTPUT

OUTPUT 'Hello World'
OUTPUT score
OUTPUT 'Score: ' + STR(score)
OUTPUT name + ', age: ' + STR(age)

String concatenation:Use + to join strings: 'Name: ' + name

Arithmetic Operators

AQA Arithmetic — All 6 Operators

Operator	Meaning	Example	Result
+	Addition	5 + 3	8
-	Subtraction	10 - 4	6
*	Multiplication	3 * 4	12
/	Division (real)	7 / 2	3.5
DIV	Integer division	7 DIV 2	3
MOD	Remainder	7 MOD 2	1

⚡ Exam Tip:DIV and MOD are frequently tested. Know that 17 DIV 5 = 3 and 17 MOD 5 = 2.

Exam Practice

Have a go at this question

AQA-style question

Write a pseudocode program that:
• Reads a number of seconds from the user
• Calculates and outputs the number of complete minutes (use DIV)
• Calculates and outputs the remaining seconds (use MOD)

4 marks

MODEL ANSWER

seconds ← INT(USERINPUT)
minutes ← seconds DIV 60
remaining ← seconds MOD 60
OUTPUT minutes
OUTPUT remaining

Key Takeaways

What to Remember

Variable = value can change · Constant = value fixed for entire program

AQA uses ← for assignment and USERINPUT (always returns a String)

DIV = integer division (floor) · MOD = remainder after division

Cast with INT() or REAL() when reading numbers from input

Variables, Constants& Operators