Boolean values (true, false, nil) in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are the three special values used to represent truthiness and absence in Ruby?

They are true (for truth), false (for falsehood), and nil (for 'nothing' or 'no value').

beginner

In Ruby, which values are considered false in conditional statements?

Only false and nil are treated as false. Everything else is true, including 0 and empty strings.

beginner

What does nil represent in Ruby?

nil means 'no value' or 'nothing here'. It is Ruby's way to say a variable or expression has no meaningful value.

beginner

How do you check if a variable is nil in Ruby?

You can use the method .nil? like variable.nil? which returns true if the variable is nil.

intermediate

What is the difference between false and nil in Ruby?

false means explicitly false, while nil means no value or absence of value. Both behave as false in conditions but have different meanings.

Which of these values is NOT considered false in Ruby?

A 0

B nil

C false

D false and nil

In Ruby, only false and nil are false. The number 0 is considered true.

What does nil represent in Ruby?

A No value or absence

B False value

C True value

D Zero number

nil means no value or absence of value in Ruby.

How can you check if a variable x is nil?

A x == false

B x == true

C x.nil?

D x == 0

The method .nil? returns true if the variable is nil.

Which of these is a Boolean value in Ruby?

A nil

B true

C 0

D "false"

true and false are Boolean values. nil is a special value meaning no value.

In Ruby, what will the expression if nil then 'yes' else 'no' end return?

A 'yes'

B error

C nil

D 'no'

Since nil is treated as false, the else branch runs, returning 'no'.

Explain the role of true, false, and nil in Ruby and how they behave in conditions.

Think about how Ruby decides if something is true or false in an if statement.

Describe how to check if a variable is nil and why this might be useful.

Consider how you know if a box is empty or not.

Practice

1. In Ruby, which of the following represents a value that means "nothing" or "no value"?

easy

A. nil

B. true

C. false

D. 0

Solution

1. Step 1: Understand the meaning of nil

   In Ruby, nil is used to represent the absence of any value, like an empty box.

2. Step 2: Compare with other options

   true and false are Boolean values meaning yes or no, but not "no value". 0 is a number, not a special value for nothing.

3. Final Answer:

   nil -> Option A

4. Quick Check:

   nil means no value [OK]

Hint: Remember: nil means no value or empty box [OK]

Common Mistakes:

• Confusing false with nil
• Thinking 0 means no value
• Mixing true and nil meanings

2. Which of the following is the correct way to write a Boolean false value in Ruby?

easy

A. False

B. FalseValue

C. FALSE

D. false

Solution

1. Step 1: Recall Ruby syntax for Boolean values

   Ruby uses lowercase true and false for Boolean values.

2. Step 2: Check each option

   False and FALSE are not valid Ruby keywords. FalseValue is not a keyword but a name.

3. Final Answer:

   false -> Option D

4. Quick Check:

   Boolean false is lowercase false [OK]

Hint: Boolean keywords are lowercase in Ruby [OK]

Common Mistakes:

• Using capitalized False or TRUE
• Adding extra words to Boolean values
• Confusing symbols with keywords

3. What will the following Ruby code print?

value = nil
if value
  puts "Yes"
else
  puts "No"
end

medium

A. nil

B. Yes

C. No

D. Error

Solution

1. Step 1: Understand how Ruby treats nil in conditions

   In Ruby, nil is treated as false in conditions.

2. Step 2: Follow the if-else logic

   Since value is nil, the if value condition is false, so the else branch runs, printing "No".

3. Final Answer:

   No -> Option C

4. Quick Check:

   nil acts as false in if [OK]

Hint: nil and false both act as false in conditions [OK]

Common Mistakes:

• Thinking nil is true
• Expecting nil to print itself
• Confusing nil with empty string

4. Find the error in this Ruby code snippet:

if false
  puts "No"
elsif nil
  puts "Maybe"
else
  puts "Yes"
end

medium

A. The condition elsif nil never runs

B. No error, prints "Yes"

C. The code prints "Maybe" incorrectly

D. Syntax error: missing end

Solution

1. Step 1: Check syntax correctness

   The code has matching if, elsif, and end, so no syntax error.

2. Step 2: Evaluate conditions in order

   false is false, nil is also false, so both conditions fail and else runs, printing "Yes".

3. Final Answer:

   No error, prints "Yes" -> Option B

4. Quick Check:

   False and nil skip to else [OK]

Hint: False and nil conditions skip to else branch [OK]

Common Mistakes:

• Thinking elsif nil runs
• Expecting syntax error
• Confusing elsif with else

5. You want to check if a variable status is either true or nil in Ruby. Which condition correctly does this?

hard

A. if status == true || status == nil

B. if status == true && status == nil

C. if status || nil

D. if status != false

Solution

1. Step 1: Understand the condition requirements

   You want to check if status is either true OR nil, so use logical OR (||).

2. Step 2: Analyze each option

   if status == true || status == nil uses status == true || status == nil, which matches the requirement. if status == true && status == nil uses AND, which can never be true for both at once. if status || nil is incorrect syntax and logic. if status != false checks if status is not false, which includes other values too.

3. Final Answer:

   if status == true || status == nil -> Option A

4. Quick Check:

   Use OR (||) to check either condition [OK]

Hint: Use || to check if either condition is true [OK]

Common Mistakes:

• Using && instead of ||
• Confusing != false with true or nil
• Writing invalid condition syntax