AQA 7517 · Paper 1 · 4.1.1c

Boolean Logic &
Boolean Operators

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

WHAT YOU'LL LEARN

AND · OR · NOT operators · Truth tables · Boolean expressions in programs

AQA SPEC LINK

4.1.1 — Use of Boolean operators in conditional statements & loops

Boolean Data Type

Boolean: True or False

A Boolean value can only be True or False. Boolean expressions use AND, OR, NOT to combine comparisons.

AND

True only if both operands are True

OR

True if at least one operand is True

NOT

Inverts the Boolean value

AND Operator

AND — Truth Table

A	B	A AND B
True	True	True
True	False	False
False	True	False
False	False	False

MNEMONIC

AND = "both must be true"
Like a security door needing BOTH a key AND a PIN code.

IN PSEUDOCODE

IF age ≥ 18 AND hasID = True THEN

OR Operator

OR — Truth Table

A	B	A OR B
True	True	True
True	False	True
False	True	True
False	False	False

MNEMONIC

OR = "at least one must be true"
Only False if BOTH are False.

IN PSEUDOCODE

IF grade = 'A' OR grade = 'B' THEN

NOT Operator

NOT — Inverting a Boolean

A	NOT A
True	False
False	True

USE CASES

IF NOT gameOver THEN ...
WHILE NOT found DO ...
IF NOT (x = y) THEN ...

NOT has highest precedence among boolean operators: NOT is evaluated first, then AND, then OR. Use brackets to clarify complex expressions.

Compound Conditions

Combining Boolean Operators

AQA EXAMPLE — Fairground Ride

height ← INT(USERINPUT)
age ← INT(USERINPUT)
IF (height ≥ 120 AND age ≥ 12) OR hasWristband = True THEN
OUTPUT "Welcome aboard!"
ELSE
OUTPUT "Not eligible"
ENDIF

⚠️ Always use brackets to make compound conditions unambiguous in the exam. AQA examiners appreciate clear structure.

Precedence

Boolean Operator Precedence

Order of evaluation (highest → lowest):

1st: NOT — evaluated first

2nd: AND

3rd: OR — evaluated last

AMBIGUOUS — AVOID

A OR B AND NOT C

Evaluates as: A OR (B AND (NOT C))

CLEARER — PREFERRED

A OR (B AND (NOT C))

Brackets make intent explicit

Application

Boolean Operators in Loops

VALIDATION LOOP EXAMPLE

score ← INT(USERINPUT)
WHILE score < 0 OR score > 100
OUTPUT "Enter a score between 0 and 100"
score ← INT(USERINPUT)
ENDWHILE
OUTPUT "Score accepted: " + STR(score)

The WHILE condition uses OR to keep looping while the input is invalid (too low OR too high). The loop exits when both conditions are False.

AQA Exam Style

Practice Question

AQA 7517 — Paper 1 Style Question

Complete the truth table for the expression: NOT A AND (B OR C)

[4 marks]

A	B	C	NOT A	B OR C	Result
T	T	F	F	T	False
T	F	F	F	F	False
F	T	F	T	T	True
F	F	F	T	F	False

Summary

Key Points to Remember

AND — True only if BOTH operands are True

OR — True if AT LEAST ONE operand is True (False only if both are False)

NOT — Inverts the Boolean; NOT True = False, NOT False = True

Precedence: NOT → AND → OR — use brackets to be safe

Boolean operators are used in IF conditions and WHILE loops to control flow

🎉 Lesson complete — move to the quiz!