Data & representation · Higher
Boolean Logic & Truth Tables
Boolean logic underpins circuits and conditions in programs. Truth tables show outputs for every input combination.
Basic gates
• **AND** – true only if all inputs true
• **OR** – true if at least one input true
• **NOT** – inverts the input
In programming, these combine conditions in IF statements.
Truth tables
List every combination of inputs (0/1) and the output.
For two inputs there are 4 rows; for three inputs, 8 rows.
Worked example
Output of A AND NOT B when A=1, B=0?
Solution: NOT B = 1; 1 AND 1 = **1**
Practice questions
1. When is AND true?
2. How many rows in a truth table with 3 inputs?