Truthy and falsy values (only nil and false are falsy) in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the variable is truthy.

Ruby

if [1]
  puts "It's truthy!"
else
  puts "It's falsy!"
end

Drag options to blanks, or click blank then click option'

Atrue

Bnil

Cfalse

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 0 as falsy because in some languages 0 is falsy.

Choosing nil or false as truthy.

In Ruby, only false and nil are falsy. Everything else, including true, is truthy.

2fill in blank

medium

Complete the code to print 'Falsy' only if the value is falsy.

Ruby

value = [1]
if !value
  puts 'Falsy'
else
  puts 'Truthy'
end

Drag options to blanks, or click blank then click option'

Afalse

B42

C"string"

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using true or other values that are truthy.

Confusing string or number as falsy.

Only false and nil are falsy in Ruby. Here, false makes the condition true after negation.

3fill in blank

hard

Fix the error in the code to correctly check for falsy values.

Ruby

if [1] == false || [1] == nil
  puts 'Falsy value'
else
  puts 'Truthy value'
end

Drag options to blanks, or click blank then click option'

Aval

Bvalue

Cfalse

Dnil

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names causing errors.

Using literal false or nil instead of variable.

The variable to check must be consistent. Using value matches the variable being tested.

4fill in blank

hard

Fill both blanks to create a hash of words and their lengths, but only include words longer than 3 characters.

Ruby

words = ["cat", "house", "dog", "elephant"]
lengths = words.select { |word| [1] [2] 3 }.map { |word| [word, [1]] }.to_h

Drag options to blanks, or click blank then click option'

Aword.length

Bword.size

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of > causing wrong filtering.

Using word instead of length method.

Use word.length to get the length and > to filter words longer than 3 characters.

5fill in blank

hard

Fill all three blanks to create a hash of uppercase words and their lengths, including only words longer than 4 characters.

Ruby

words = ["apple", "bat", "carrot", "dog"]
result = words.select { |w| [2] [3] 4 }.map { |w| [[1], [2]] }.to_h

Drag options to blanks, or click blank then click option'

Aw.upcase

Bw.length

C>

Dw

Attempts:

3 left

💡 Hint

Common Mistakes

Using the word itself as key instead of uppercase.

Using less than operator causing wrong filtering.

Use w.upcase as the key, w.length as the value, and filter words with length greater than 4.

Practice

1. In Ruby, which of the following values is considered falsy?

easy

A. false

B. 0

C. "" (empty string)

D. [] (empty array)

Solution

1. Step 1: Recall Ruby falsy values

   In Ruby, only false and nil are falsy.

2. Step 2: Check each option

   0, empty string, and empty array are all truthy in Ruby.

3. Final Answer:

   false -> Option A

4. Quick Check:

   Falsy = false or nil [OK]

Hint: Only false and nil are falsy in Ruby [OK]

Common Mistakes:

• Thinking 0 is falsy like in some other languages
• Assuming empty string is falsy
• Confusing empty array with falsy

2. Which of the following is the correct way to check if a variable x is truthy in Ruby?

easy

A. if x == true

B. if x

C. if x != nil

D. if x == nil

Solution

1. Step 1: Understand Ruby truthy check

   In Ruby, if x automatically checks if x is truthy (not false or nil).

2. Step 2: Analyze options

   if x == true only matches true, missing other truthy values; if x != nil treats false as truthy (false != nil); if x == nil checks the opposite of truthy.

3. Final Answer:

   if x -> Option B

4. Quick Check:

   Use if x for truthy check [OK]

Hint: Use 'if x' to check truthiness simply [OK]

Common Mistakes:

• Using 'if x == true' which misses other truthy values
• Using 'if x != nil' which treats false as truthy
• Checking 'if x == nil' to test truthiness

3. What will be the output of this Ruby code?

value = 0
if value
  puts "Truthy"
else
  puts "Falsy"
end

medium

A. No output

B. Falsy

C. Error

D. Truthy

Solution

1. Step 1: Identify the value and condition

   The variable value is assigned 0. The if value checks if value is truthy.

2. Step 2: Recall Ruby truthy rules

   In Ruby, 0 is truthy, so the if branch runs.

3. Final Answer:

   Truthy -> Option D

4. Quick Check:

   0 is truthy in Ruby [OK]

Hint: Remember 0 is truthy in Ruby, unlike some languages [OK]

Common Mistakes:

• Assuming 0 is falsy like in other languages
• Expecting else branch to run
• Confusing output with error

4. The following Ruby code is intended to print "Falsy" only when var is falsy. What is wrong?

var = nil
if var == false
  puts "Falsy"
else
  puts "Truthy"
end

medium

A. It should check 'if var == nil' only

B. Syntax error in the if statement

C. It misses the case when var is nil, which is also falsy

D. It should use 'var != false' instead

Solution

1. Step 1: Understand falsy values in Ruby

   Both false and nil are falsy in Ruby.

2. Step 2: Analyze the condition

   The code checks only var == false, so it misses nil which is also falsy.

3. Final Answer:

   It misses the case when var is nil, which is also falsy -> Option C

4. Quick Check:

   Falsy = false or nil [OK]

Hint: Check both false and nil for falsy, not just false [OK]

Common Mistakes:

• Checking only for false and ignoring nil
• Confusing syntax errors with logic errors
• Using wrong comparison operators

5. You want to filter out falsy values from this array in Ruby:

arr = [false, nil, 0, "", [], true]

Which code correctly returns only truthy values?

hard

A. arr.select { |v| v }

B. arr.reject { |v| v }

C. arr.select { |v| v != false }

D. arr.select { |v| v == true }

Solution

1. Step 1: Understand filtering truthy values

   Using select { |v| v } keeps only truthy values because v in condition is true for truthy values.

2. Step 2: Analyze other options

   arr.select { |v| v != false } keeps nil (nil != false); arr.reject { |v| v } rejects truthy values; arr.select { |v| v == true } keeps only true, missing other truthy values.

3. Final Answer:

   arr.select { |v| v } -> Option A

4. Quick Check:

   Use select with block returning value for truthy filter [OK]

Hint: Use select { |v| v } to keep truthy values [OK]

Common Mistakes:

• Using reject instead of select
• Checking explicitly for false instead of truthiness
• Selecting only true, missing other truthy values