Predicate methods (ending with ?) in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using a predicate method?

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

Ruby

def even_or_odd?(num)
  num.even?
end

puts even_or_odd?(7)

A 7

B true

C false

D nil

💡 Hint

Remember, the method checks if the number is even.

The method calls num.even? which returns true if num is even, false otherwise. Since 7 is odd, it returns false.

❓ Predict Output

intermediate

What does this predicate method return?

What will be the output of this Ruby code?

Ruby

class String
  def has_vowels?
    !!(self =~ /[aeiou]/i)
  end
end

puts "sky".has_vowels?

A true

B false

C nil

D 0

💡 Hint

Check if the string contains any vowels.

The method returns true if the string contains vowels, false otherwise. "sky" has no vowels, so it returns false.

🔧 Debug

advanced

Why does this predicate method raise an error?

This Ruby code raises an error. What is the cause?

Ruby

def positive?(num)
  num > 0 ? true : false
end

puts positive?(nil)

A NoMethodError because nil can't be compared with >

B SyntaxError due to missing colon in ternary

C Returns false because nil is not positive

D Returns true because nil is treated as zero

💡 Hint

Think about what happens when you compare nil with a number.

The expression num > 0 fails because nil does not support comparison with >, causing a NoMethodError.

🧠 Conceptual

advanced

What is the purpose of predicate methods ending with '?' in Ruby?

Why do Ruby methods often end with a question mark '?'? Choose the best explanation.

A They indicate the method modifies the object

B They are used only for methods that ask user input

C They are private methods by convention

D They always return a boolean value indicating true or false

💡 Hint

Think about what the '?' symbol suggests in English.

In Ruby, methods ending with '?' are predicate methods that return true or false, indicating a yes/no question about the object.

❓ Predict Output

expert

What is the output of this complex predicate method?

Analyze the code and determine what it prints.

Ruby

class Array
  def all_even?
    all?(&:even?)
  end
end

arr = [2, 4, 6, 7]
puts arr.all_even?

A false

B NoMethodError

C nil

D true

💡 Hint

Check if every element in the array is even.

The method all_even? returns true only if all elements are even. Since 7 is odd, it returns false.