Truthy and falsy values (only nil and false are falsy) in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code?

Consider the following Ruby code snippet. What will it print?

Ruby

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

A Truthy

B Falsy

C SyntaxError

D nil

💡 Hint

Remember in Ruby, only nil and false are falsy.

In Ruby, 0 is considered truthy, so the if condition passes and prints 'Truthy'.

❓ Predict Output

intermediate

What does this Ruby code print?

Look at this Ruby code. What will be printed?

Ruby

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

A Truthy

B Falsy

C nil

D RuntimeError

💡 Hint

Empty strings are not false or nil in Ruby.

Empty strings are truthy in Ruby, so the code prints 'Truthy'.

❓ Predict Output

advanced

What is the output of this Ruby code with logical operators?

What will this Ruby code print?

Ruby

a = false
b = nil
c = true
if a || b || c
  puts "Truthy"
else
  puts "Falsy"
end

A Falsy

B Truthy

C nil

D SyntaxError

💡 Hint

Only false and nil are falsy; true is truthy.

The expression a || b || c evaluates to true because c is true, so it prints 'Truthy'.

❓ Predict Output

advanced

What does this Ruby code print when using the not operator?

Analyze this Ruby code and determine its output.

Ruby

value = nil
if !value
  puts "Truthy"
else
  puts "Falsy"
end

A nil

B TypeError

C Falsy

D Truthy

💡 Hint

The not operator (!) inverts truthiness.

Since value is nil (falsy), !value is true, so it prints 'Truthy'.

🧠 Conceptual

expert

Which value is falsy in Ruby?

Select the only value that is falsy in Ruby.

A 0

B "false"

C nil

D []

💡 Hint

Only nil and false are falsy in Ruby.

In Ruby, only nil and false are falsy; all other values including 0, empty string, and empty array are truthy.

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