� Boolean Logic: True or False?

What You’ll Learn

By the end of this lesson, you will:

  • Know what boolean values are (true and false)
  • Use comparison operators like == and !=
  • Understand how computers make decisions
  • Practice with an interactive calculator

What Are Booleans?

Booleans are simple: they can only be true or false. Think of them like light switches - they’re either ON or OFF.

Examples:

  • true = yes, on, correct
  • false = no, off, incorrect

Computers use booleans to make decisions, just like you do every day!

Basic Boolean Operations

Comparing Numbers

console.log(5 == 5);     // true - equal
console.log(5 != 3);     // true - not equal
console.log(7 > 3);      // true - greater than
console.log(2 < 8);      // true - less than

Combining Conditions

// AND (&&) - BOTH must be true
console.log(true && true);    // true
console.log(true && false);   // false

// OR (||) - AT LEAST ONE must be true
console.log(true || false);   // true
console.log(false || false);  // false

// NOT (!) - FLIPS the value
console.log(!true);           // false
console.log(!false);          // true

Try It Out: Interactive Calculator

See how booleans work in a real calculator:

0
AC
+/-
%
÷
7
8
9
*
4
5
6
-
1
2
3
+
0
.
=

What’s Happening Behind the Scenes?

Calculator Status

Last Action: None

Calculator Checks:

  • Ready for new number: true
  • Has decimal point: false
  • Number stored in memory: false
  • Operation waiting: false

How the Calculator Uses Booleans

The calculator makes decisions using true/false questions:

// When you click a number button:
if (readyForNewNumber == true) {
    // Show the new number
    display = newNumber;
} else {
    // Add to existing number
    display = display + newNumber;
}

// When you click an operation (+, -, *, /):
if (hasStoredNumber == false) {
    // Store the first number
    storedNumber = currentNumber;
} else {
    // Calculate with stored number
    result = calculate(storedNumber, currentNumber);
}

Practice Exercises

Exercise 1: Predict the Result

Try to guess what these will show before testing:

  1. 5 == 5 → ?
  2. 3 > 7 → ?
  3. true && false → ?
  4. true || false → ?
  5. !true → ?

Exercise 2: Real-World Examples

Think about these everyday decisions as booleans:

  • “If it’s raining AND I don’t have an umbrella, then I’ll get wet”
  • “If I have homework OR there’s a test tomorrow, then I need to study”
  • “If it’s NOT a school day, then I can sleep in”

Boolean Truth Tables

Quick reference for how booleans combine:

AND (&&) - Both must be true

| A | B | Result | |—|—|——–| | true | true | true | | true | false | false | | false | true | false | | false | false | false |

OR (||) - At least one must be true

| A | B | Result | |—|—|———-| | true | true | true | | true | false | true | | false | true | true | | false | false | false |

Why Booleans Matter

Booleans are everywhere in programming! They help computers:

  • Make decisions (if this, then that)
  • Check conditions (is the password correct?)
  • Control what happens next in a program

Quick Quiz

  1. What are the only two boolean values?
  2. What does 5 > 3 equal?
  3. What does true && false equal?
  4. Give an example of a boolean question from everyday life.

Answers: 1) true and false, 2) true, 3) false, 4) “Is it raining?” or “Am I hungry?”

Great job! You now understand boolean logic - the foundation of how computers make decisions!