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Boolean Logic Explained – Truth Tables & Logical Expressions (O Level Computer Science 2210 / IGCSE 0478)

What Is Boolean Logic?

Boolean logic is a system of logic used in computers where values can only be True or False.

In digital systems, these values are represented using binary numbers:

  • True = 1

  • False = 0

Boolean logic is used to control decision-making in programs and digital circuits.

It forms the foundation of:

  • Logic gates

  • Computer processors

  • Conditional statements in programming

Boolean Variables

A Boolean variable stores one of two possible values:

TRUE
FALSE

Example in programming:

isLoggedIn ← TRUE

Boolean variables are commonly used in conditions and decision-making statements.

Boolean Operators

Boolean logic uses operators to combine or compare conditions.

OperatorMeaningANDBoth conditions must be trueORAt least one condition must be trueNOTReverses the value

Example expression:

A AND B

This expression is true only when both A and B are true.

Truth Tables

A truth table shows the output of a logical expression for all possible combinations of inputs.

Truth tables help programmers and engineers analyze logical operations.

Example: AND Operator

ABA AND B000010100111

The result is 1 only when both inputs are 1.

Example: OR Operator

ABA OR B000011101111

The result is 1 when at least one input is 1.

Example: NOT Operator

ANOT A0110

The NOT operator reverses the value.

Boolean Logic in Programming

Boolean logic is widely used in programming.

Example:

IF temperature > 30 THEN
    OUTPUT "Hot"
END IF

The condition temperature > 30 evaluates to either TRUE or FALSE.

This determines whether the program executes the instruction.

Why Boolean Logic Is Important

Boolean logic allows computers to:

  • Make logical decisions

  • Control program flow

  • Process digital signals

  • Build complex circuits

Every modern computer relies heavily on Boolean logic for processing information.

Exam Tip (2210 / 0478)

Students are often asked to:

  • Define Boolean logic

  • Complete truth tables

  • Evaluate logical expressions

A common exam question is:

Complete the truth table for the expression A OR B.

Practice Question

Explain one purpose of a truth table.

Answer

A truth table shows all possible input combinations and the resulting output of a logical expression or logic gate.

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