Variable-length arguments (*args) in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of method using *args with sum

What is the output of this Ruby code?

def sum_all(*numbers)
  numbers.reduce(0) { |sum, n| sum + n }
end

puts sum_all(1, 2, 3, 4)

Ruby

def sum_all(*numbers)
  numbers.reduce(0) { |sum, n| sum + n }
end

puts sum_all(1, 2, 3, 4)

A Error: wrong number of arguments

B 1234

C 10

D nil

💡 Hint

Remember *args collects all arguments into an array.

The method sum_all collects all arguments into an array called numbers. Then it sums them using reduce starting from 0. So 1+2+3+4 = 10.

❓ Predict Output

intermediate

Output when mixing fixed and variable arguments

What will this Ruby code print?

def greet(greeting, *names)
  names.map { |name| "#{greeting}, #{name}!" }
end

puts greet("Hello", "Alice", "Bob").join(", ")

Ruby

def greet(greeting, *names)
  names.map { |name| "#{greeting}, #{name}!" }
end

puts greet("Hello", "Alice", "Bob").join(", ")

A Hello, Alice!, Hello, Bob!

B Hello, Alice, Bob!

C Error: wrong number of arguments

D Hello, !, Hello, !

💡 Hint

The first argument is fixed, the rest go into *names.

The method takes a fixed greeting and any number of names. It returns an array of greetings for each name. Joining with ', ' prints them separated by commas.

🔧 Debug

advanced

Identify the error in this method using *args

What error does this Ruby code raise?

def multiply(*nums)
  nums * nums
end

puts multiply(3, 4)

Ruby

def multiply(*nums)
  nums * nums
end

puts multiply(3, 4)

A TypeError: Array can't be coerced into Integer

B NoMethodError: undefined method '*' for Array

C SyntaxError: unexpected '*'

D Output: [6, 8]

💡 Hint

What happens when you multiply an array by another array in Ruby?

In Ruby, multiplying an array by an integer repeats the array elements. But here nums is an array and nums * nums tries to multiply array by array, causing a TypeError.

📝 Syntax

advanced

Which method definition correctly uses *args?

Which of these Ruby method definitions correctly accepts any number of arguments?

A def example(*args); args.each + 1; end

B def example(*args); args.sum; end

C def example(*args); args + 1; end

D def example(args*); args.sum; end

💡 Hint

Look for correct syntax and valid operations on args.

Option B correctly defines *args and sums the array. B has invalid syntax. C tries to add 1 to an array causing error. D tries to add 1 to an enumerator causing error.

🚀 Application

expert

What is the output of this recursive method using *args?

Consider this Ruby code:

def recursive_sum(*nums)
  return 0 if nums.empty?
  nums[0] + recursive_sum(*nums[1..])
end

puts recursive_sum(5, 10, 15)

What is the output?

Ruby

def recursive_sum(*nums)
  return 0 if nums.empty?
  nums[0] + recursive_sum(*nums[1..])
end

puts recursive_sum(5, 10, 15)

A nil

B Error: stack level too deep

C 15

D 30

💡 Hint

The method sums the first number plus the sum of the rest recursively.

The method recursively sums all numbers by adding the first element to the sum of the rest until no numbers remain. So 5 + 10 + 15 = 30.