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.

Practice

1. What does *args do in a Ruby method?

easy

A. Makes the method return an array

B. Restricts the method to accept only one argument

C. Converts all arguments to strings automatically

D. Allows the method to accept any number of arguments as an array

Solution

1. Step 1: Understand the role of *args

   *args collects all extra arguments passed to a method into an array.

2. Step 2: Recognize the flexibility it provides

   This lets the method accept any number of arguments, not just one fixed number.

3. Final Answer:

   Allows the method to accept any number of arguments as an array -> Option D

4. Quick Check:

   *args = variable number of arguments [OK]

Hint: Remember *args packs all extra inputs into an array [OK]

Common Mistakes:

• Thinking *args limits arguments to one
• Confusing *args with return values
• Assuming *args converts types automatically

2. Which of the following is the correct syntax to define a method that accepts variable-length arguments in Ruby?

easy

A. def example(args*)

B. def example(args)

C. def example(*args)

D. def example(&args)

Solution

1. Step 1: Identify the correct syntax for variable-length arguments

   In Ruby, *args is used inside method parentheses to accept any number of arguments.

2. Step 2: Check each option

   def example(*args) is the correct syntax. def example(args*) places the asterisk incorrectly. def example(args) accepts only one argument. def example(&args) uses & which is for blocks.

3. Final Answer:

   def example(*args) -> Option C

4. Quick Check:

   Method with *args = correct syntax [OK]

Hint: Look for asterisk before argument name inside parentheses [OK]

Common Mistakes:

• Placing * after the argument name
• Using & instead of * for arguments
• Omitting the asterisk entirely

3. What will be the output of the following Ruby code?

def greet(*names)
  names.join(", ")
end

puts greet("Alice", "Bob", "Carol")

medium

A. Alice, Bob, Carol

B. ["Alice", "Bob", "Carol"]

C. Alice Bob Carol

D. Error: wrong number of arguments

Solution

1. Step 1: Understand how *names works

   The method collects all arguments into an array called names. Here, it will be ["Alice", "Bob", "Carol"].

2. Step 2: Analyze the join method

   names.join(", ") joins array elements into a string separated by ", ". So the output is "Alice, Bob, Carol".

3. Final Answer:

   Alice, Bob, Carol -> Option A

4. Quick Check:

   Array joined with commas = Alice, Bob, Carol [OK]

Hint: Remember join adds separator between array elements [OK]

Common Mistakes:

• Expecting space-separated output without commas
• Thinking *args returns array string representation
• Assuming error due to multiple arguments

4. Identify the error in this Ruby method definition:

def sum_numbers(*nums)
  total = 0
  nums.each do |n|
    total += n
  end
  total
end

puts sum_numbers(1, 2, '3')

medium

A. Syntax error in method definition

B. Cannot add string '3' to integer total

C. Missing return statement

D. Method does not accept variable arguments

Solution

1. Step 1: Check method logic with variable arguments

   The method sums all numbers in nums using total += n.

2. Step 2: Identify type mismatch error

   Passing '3' as a string causes an error when adding to integer total. Ruby cannot add string and integer directly.

3. Final Answer:

   Cannot add string '3' to integer total -> Option B

4. Quick Check:

   Adding string to integer causes error [OK]

Hint: Check argument types when summing inside *args method [OK]

Common Mistakes:

• Ignoring type mismatch between string and integer
• Assuming method needs explicit return
• Thinking *args causes syntax error

5. You want to write a Ruby method combine that accepts any number of arrays and returns a single array with all elements combined. Which method definition correctly uses *args to achieve this?

hard

A. def combine(*arrays)
arrays.flatten
end

B. def combine(arrays)
arrays.flatten
end

C. def combine(*arrays)
arrays.join
end

D. def combine(*arrays)
arrays.map(&:size)
end

Solution

1. Step 1: Understand the goal

   The method should accept multiple arrays and combine all their elements into one flat array.

2. Step 2: Analyze each option

   def combine(*arrays) arrays.flatten end uses *arrays to accept variable arrays and calls flatten to merge them into one array. def combine(arrays) arrays.flatten end accepts only one argument (an array of arrays). def combine(*arrays) arrays.join end joins arrays into a string, not desired. def combine(*arrays) arrays.map(&:size) end returns sizes, not combined elements.

3. Final Answer:

   def combine(*arrays) arrays.flatten end -> Option A

4. Quick Check:

   Use *args and flatten to combine arrays [OK]

Hint: Use *args plus flatten to merge multiple arrays [OK]

Common Mistakes:

• Not using *args for multiple arrays
• Using join instead of flatten
• Returning sizes instead of combined elements