Array creation methods in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code creating an array?

Consider the following Ruby code that creates an array. What will be printed?

Ruby

arr = Array.new(3, 'cat')
arr[0].upcase!
puts arr.inspect

A ["cat", "cat", "cat"]

B ["CAT", "CAT", "CAT"]

C ["CAT", "cat", "cat"]

D ["cat", "CAT", "cat"]

💡 Hint

Think about how Array.new with a single object argument shares the same object.

Using Array.new(3, 'cat') creates an array with three references to the same string object. When upcase! modifies the first element, it changes the shared string, so all elements show the change.

❓ Predict Output

intermediate

What does this Ruby array creation code output?

What will be the output of this Ruby code snippet?

Ruby

arr = Array.new(3) { 'dog' }
arr[0].upcase!
puts arr.inspect

A ["DOG", "dog", "dog"]

B ["DOG", "DOG", "DOG"]

C ["dog", "dog", "dog"]

D ["dog", "DOG", "dog"]

💡 Hint

Consider how the block form of Array.new creates new objects.

Using Array.new(3) { 'dog' } creates a new string object for each element. So modifying one element does not affect the others.

🧠 Conceptual

advanced

Which Ruby array creation method creates independent objects?

Which of the following Ruby array creation methods ensures each element is a separate object?

A Array.new(4, [])

B Array.new(4)

C Array.new(4) { [] }

D Array.new(4, nil)

💡 Hint

Think about how the block form works compared to the single object argument.

Array.new(4) { [] } calls the block 4 times, creating a new empty array each time. The other methods either share the same object or fill with nil.

❓ Predict Output

advanced

What is the output of this Ruby array creation and modification?

What will this Ruby code print?

Ruby

arr = Array.new(2) { |i| i * 2 }
arr[1] = 10
puts arr.inspect

A [0, 10]

B [0, 1]

C [0, 2]

D [2, 10]

💡 Hint

Remember the block argument is the index of the element.

The block { |i| i * 2 } creates [0, 2]. Then arr[1] = 10 changes the second element to 10.

🔧 Debug

expert

Why does this Ruby array creation code raise an error?

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

Ruby

arr = Array.new(3) { |i| i + 'a' }
puts arr.inspect

A NameError because 'i' is undefined

B SyntaxError due to missing parentheses

C No error, outputs ["0a", "1a", "2a"]

D TypeError because you cannot add an integer and a string

💡 Hint

Check the operation inside the block carefully.

The block tries to add an integer i to a string 'a', which causes a TypeError in Ruby.