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Programming Basics

Boolean Logic (and/or/not)

The idea, in plain English

A boolean is just a yes/no, true/false light switch. Boolean LOGIC is how you combine switches. AND needs BOTH switches on to be true. OR needs AT LEAST ONE switch on. NOT just flips a switch to its opposite.

How it works

  1. 1`and` (written `&&` in JavaScript) is true only when both sides are true — like needing both a ticket AND being old enough.
  2. 2`or` (written `||` in JavaScript) is true when at least one side is true — like being let in for being a member OR being a kid.
  3. 3`not` (written `!` in JavaScript) flips a true into false, or a false into true.

When you'd use it

Use boolean logic any time a decision depends on combining more than one yes/no condition. Examples: checking permissions, validating a form, or deciding whether a game character can move.

Common beginner mistakes

  • Mixing up `and` and `or`. 'And' is stricter — it needs everything true. 'Or' is looser — it needs just one true.
  • Printing a raw `true`/`false` value straight into a sentence. It usually reads better to turn it into a word like 'yes' or 'no' first.

Try it — edit and run

Click the code to edit · press ⌘/Ctrl+↵ to run

Editable code. Tab and Shift+Tab indent. Press Escape, then Tab, to move focus out of the editor.

Expected output — hit Run to try it
Can watch (14, has ticket): yes
Can watch (10, has ticket): no
Can enter free (member, not kid): yes
Need umbrella: yes

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