Boolean Examples in CS Thinking

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Boolean.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in CS Thinking.

Concept Recap

A data type representing a logical value that can only be true or false—nothing else. Booleans are produced by comparison operators (==, <, >, !=) and consumed by control structures (if-statements, while-loops) to make decisions.

A boolean is a yes/no answer. Is the user logged in? True or false. Is the number positive? True or false.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Booleans are the language of decisions. Every if-statement evaluates a boolean condition.

Common stuck point: 0, empty string, None/null, and empty lists are often 'falsy' — they act like False in conditions even though they're not boolean.

Sense of Study hint: When working with booleans, remember that comparison operators like ==, <, and > return boolean values. You can combine booleans using AND, OR, and NOT. Be careful with 'truthy' and 'falsy' values—in many languages, 0, empty strings, and null are treated as False in conditions.

Worked Examples

Example 1

easy
Evaluate each expression when x = 7: (a) x > 5, (b) x == 10, (c) x != 7, (d) x >= 7.

Answer

(a) TRUE, (b) FALSE, (c) FALSE, (d) TRUE.

First step

1
Step 1: Substitute x=7x = 7 into each comparison.

Full solution

  1. 2
    Step 2: Evaluate (a) 7>5→7 > 5 \to TRUE and (b) 7==10→7 == 10 \to FALSE.
  2. 3
    Step 3: Evaluate (c) 7!=7→7 != 7 \to FALSE and (d) 7>=7→7 >= 7 \to TRUE.
Boolean expressions evaluate to TRUE or FALSE. They are the foundation of conditions in IF statements, loops, and filters. The operators >, <, ==, !=, >=, <= compare values.

Example 2

medium
A variable `isLoggedIn` is a boolean. Write pseudocode that outputs 'Welcome back' if logged in, or 'Please log in' otherwise.

Example 3

medium
A pseudocode block reads: IF age >= 13 AND age <= 19 THEN print 'teenager'. For age = 12, does it print?

Example 4

medium
A student writes `if score = 90:` in Python instead of `if score == 90:`. What goes wrong?

Example 5

medium
A coupon condition: total >= 50 AND (memberSince < 2020 OR isStudent). For total=60, memberSince=2022, isStudent=True, does the coupon apply?

Example 6

hard
Trace: x = 0; if x or 'no value': print('ran'); does it print?

Example 7

hard
Trace: nums = [0, 1, 2]; any(nums) returns?

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
What is the value of each: (a) NOT TRUE, (b) (5 < 3) OR (10 > 8), (c) (4 == 4) AND (3 > 5)?

Example 2

medium
A theme park ride requires: age ≥ 12 AND height ≥ 140. A child is age 13 and height 135. Evaluate the full Boolean expression step by step. Can they ride?

Example 3

easy
Evaluate `True AND False`.

Example 4

easy
Evaluate `True OR False`.

Example 5

easy
Evaluate `NOT True`.

Example 6

easy
Evaluate the comparison `5 > 3`.

Example 7

easy
Evaluate `4 == 4`.

Example 8

easy
Evaluate `7 != 7` (not-equal).

Example 9

easy
Evaluate `False OR False`.

Example 10

easy
Evaluate `NOT (3 < 2)`.

Example 11

medium
Evaluate `(5 > 3) AND (2 == 2)`.

Example 12

medium
Evaluate `(4 < 2) OR (6 >= 6)`.

Example 13

medium
Apply De Morgan: simplify `NOT (A AND B)`.

Example 14

medium
Evaluate XOR: `True XOR True` (true when operands differ).

Example 15

medium
Short-circuit: in `False AND f()`, is `f()` called? Why?

Example 16

medium
Truthy/falsy: in `if 0:` does the body run? What about `if "hi":`?

Example 17

medium
Style: rewrite `if x == True:` to use `x` directly. What is the cleaner form?

Example 18

medium
Evaluate `NOT True OR False` given NOT binds tighter than OR.

Example 19

medium
Evaluate `(3 == 3) AND (4 > 5) OR (1 < 2)` (AND before OR).

Example 20

challenge
Evaluate `NOT (A OR B)` when `A = False`, `B = True`, then verify with De Morgan.

Example 21

challenge
Short-circuit safety: explain why `if x != 0 AND 10 / x > 1:` ordering matters.

Example 22

challenge
Build a truth table count: for how many of the 4 input pairs (A,B) is `A XOR B` True?

Example 23

easy
What are the only two values a boolean variable can hold?

Example 24

easy
Evaluate when x = 10: x < 20.

Example 25

easy
Evaluate when n = 5: n != 5.

Example 26

easy
Evaluate: (8 >= 8).

Example 27

easy
What boolean value does the expression 3 > 5 produce?

Example 28

easy
Evaluate `NOT (5 == 5)`.

Example 29

medium
Evaluate when a=4, b=7: (a < b) AND (b < 10).

Example 30

medium
In Python, what does `bool([])` return?

Example 31

medium
In Python, what does `bool('False')` return?

Example 32

medium
Pseudocode: WHILE NOT done DO …. If done starts as True, how many times does the body run?

Example 33

medium
Evaluate (3 < x) AND (x < 10) when x = 3.

Example 34

medium
Evaluate (True AND False) OR (True AND True).

Example 35

medium
In Python, what does `(False or 7)` evaluate to?

Example 36

hard
What does Python print: `print(True + True + False)`?

Example 37

hard
A function returns the boolean `n > 0 and n % 2 == 0`. For n = -4, what does it return?

Example 38

hard
A login pseudocode: ok = (user == 'admin') AND (password == 'pw1'). Why is testing `if ok == True:` worse style than `if ok:`?

Example 39

challenge
In Python, what does `not '' and 'hi'` evaluate to?
← Back to Boolean Practice Mode

Background Knowledge

These ideas may be useful before you work through the harder examples.

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