Bang 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 bang method?

Consider the following Ruby code snippet. What will be printed?

Ruby

arr = [1, 2, 3]
arr.reverse!
puts arr.inspect

A nil

B [1, 2, 3]

C Error: undefined method 'reverse!'

D [3, 2, 1]

💡 Hint

Bang methods usually modify the object itself.

The reverse! method reverses the array in place, changing arr to [3, 2, 1].

❓ Predict Output

intermediate

What does this string bang method return?

What will be the output of this Ruby code?

Ruby

str = "hello"
result = str.upcase!
puts result
puts str

A

nil
hello

B

HELLO
hello

C

HELLO
HELLO

D Error: undefined method 'upcase!'

💡 Hint

upcase! changes the string itself and returns the modified string.

upcase! converts str to uppercase in place and returns the modified string.

❓ Predict Output

advanced

What is the output when bang method does not change the object?

Look at this Ruby code. What will be printed?

Ruby

arr = [1, 2, 3]
result = arr.sort!
puts result.inspect
puts arr.inspect

A

nil
[1, 2, 3]

B

[1, 2, 3]
[1, 2, 3]

C

[3, 2, 1]
[3, 2, 1]

D Error: undefined method 'sort!'

💡 Hint

Bang methods return nil if no changes were made.

Since arr is already sorted, sort! returns nil and arr stays the same.

❓ Predict Output

advanced

What error does this code raise?

What error will this Ruby code produce?

Ruby

num = 10
num.negate!

A NoMethodError: undefined method 'negate!' for 10:Integer

B SyntaxError: unexpected '!'

C TypeError: can't convert Integer to String

D RuntimeError: method negate! failed

💡 Hint

Check if Integer has a negate! method.

Integer class does not have a negate! method, so NoMethodError is raised.

🧠 Conceptual

expert

Why do Ruby bang methods sometimes return nil?

In Ruby, some bang methods return nil instead of the modified object. Why does this happen?

A Because the method always returns nil by design

B Because the method did not make any changes to the object

C Because the object is frozen and cannot be changed

D Because the method encountered an error during execution

💡 Hint

Think about what happens if the object is already in the desired state.

Bang methods return nil when no changes are made to signal the object was unchanged.