Parameters with default values in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of method with default parameters

What is the output of this Ruby code?

Ruby

def greet(name = "Guest", greeting = "Hello")
  "#{greeting}, #{name}!"
end

puts greet("Alice")

A Hello, Guest!

B Alice, Hello!

C Hello, Alice!

D Error: wrong number of arguments

💡 Hint

Check which parameters are given and which use default values.

The method greet has two parameters with default values. When called with one argument, the first parameter is set to "Alice" and the second uses its default "Hello". So the output is "Hello, Alice!".

❓ Predict Output

intermediate

Method call with all default parameters

What will this Ruby code print?

Ruby

def calculate(a = 5, b = 10)
  a * b
end

puts calculate

A 50

B 15

C Error: wrong number of arguments

D 0

💡 Hint

No arguments are passed, so all default values are used.

Both parameters a and b use their default values 5 and 10. The method returns 5 * 10 = 50.

🔧 Debug

advanced

Identify the error in method with default parameters

What error does this Ruby code raise when run?

Ruby

def add(x, y = 2, z)
  x + y + z
end

puts add(1, 3, 4)

A No error, outputs 8

B SyntaxError: default argument followed by non-default argument

C TypeError: undefined method '+' for nil:NilClass

D ArgumentError: wrong number of arguments (given 3, expected 2)

💡 Hint

In Ruby, parameters with default values must come after parameters without defaults.

Ruby does not allow a parameter with a default value (y=2) to be followed by a parameter without a default (z). This causes a SyntaxError.

❓ Predict Output

advanced

Output with mixed default and explicit parameters

What is the output of this Ruby code?

Ruby

def info(name = "Unknown", age = 0, city = "Nowhere")
  "#{name} is #{age} years old and lives in #{city}."
end

puts info("Bob", city: "Paris")

A Bob is city: Paris years old and lives in Nowhere.

B Bob is 0 years old and lives in Nowhere.

C Bob is 0 years old and lives in Paris.

D Error: wrong number of arguments

💡 Hint

Check how Ruby handles keyword arguments versus positional arguments.

The method expects positional arguments, but city: "Paris" is a keyword argument. Ruby raises an ArgumentError because the method does not accept keyword arguments.

🧠 Conceptual

expert

Number of parameters in method with defaults and splat

Given this Ruby method, how many arguments can it accept without error?

Ruby

def example(a, b = 2, *c, d)
  [a, b, c, d]
end

A At least 2 arguments, no maximum limit

B Exactly 4 arguments only

C At least 3 arguments, no maximum limit

D At least 1 argument, no maximum limit

💡 Hint

Consider required, optional, splat, and default parameters in Ruby.

'a' is required. 'b' has a default value, making it optional. '*c' collects any number (including zero) of additional arguments. 'd' is a required positional parameter after the splat. Therefore, at least 2 arguments are required (one for 'a' and one for 'd'), with no maximum due to the splat '*c'.

Practice

1. What does a default parameter value in a Ruby method do?
def greet(name = "Guest")

easy

A. It causes a syntax error if the argument is missing.

B. It makes the parameter mandatory every time the method is called.

C. It changes the method name automatically.

D. It allows the method to be called without that argument, using the default instead.

Solution

1. Step 1: Understand default parameter purpose

   Default parameters provide a fallback value if no argument is given.

2. Step 2: Apply to the example method

   In def greet(name = "Guest"), if no name is passed, "Guest" is used.

3. Final Answer:

   It allows the method to be called without that argument, using the default instead. -> Option D

4. Quick Check:

   Default parameter = fallback value [OK]

Hint: Default means optional argument with fallback value [OK]

Common Mistakes:

• Thinking default parameters are mandatory
• Assuming missing arguments cause errors
• Confusing default values with method overloading

2. Which of the following is the correct syntax to define a method with a default parameter in Ruby?

easy

A. def add(a, b = 5); a + b; end

B. def add(a =, b 5); a + b; end

C. def add(a, b: 5); a + b; end

D. def add(a, b); b = 5; a + b; end

Solution

1. Step 1: Review Ruby default parameter syntax

   Default values are set with = value after the parameter name.

2. Step 2: Check each option

   def add(a, b = 5); a + b; end uses b = 5 correctly. def add(a =, b 5); a + b; end has invalid syntax. def add(a, b: 5); a + b; end uses keyword argument style, not default parameter. def add(a, b); b = 5; a + b; end assigns inside method body, not default parameter.

3. Final Answer:

   def add(a, b = 5); a + b; end -> Option A

4. Quick Check:

   Default param syntax = param = value [OK]

Hint: Use = after parameter name for default values [OK]

Common Mistakes:

• Using colon instead of equals for default values
• Placing = before parameter name
• Assigning default inside method body instead of parameter list

3. What is the output of this Ruby code?

def multiply(x, y = 2)
  x * y
end

puts multiply(4)
puts multiply(4, 3)

medium

A. 8\n12

B. 4\n7

C. Error: missing argument

D. 6\n12

Solution

1. Step 1: Analyze method calls with default parameter

   First call: multiply(4) uses default y=2, so 4*2=8. Second call: multiply(4,3) uses y=3, so 4*3=12.

2. Step 2: Determine output of puts statements

   Outputs are printed on separate lines: 8 then 12.

3. Final Answer:

   8 12 -> Option A

4. Quick Check:

   Default param used when missing = 8, explicit param = 12 [OK]

Hint: Default used if argument missing, else given value [OK]

Common Mistakes:

• Expecting error when argument is missing
• Confusing default parameter with keyword arguments
• Mixing up output values

4. Identify the error in this Ruby method definition:

def greet(name = "Guest", age)
  "Hello #{name}, you are #{age} years old."
end

medium

A. Method name cannot be 'greet' with parameters.

B. Missing return statement causes error.

C. Default parameters must come after non-default parameters.

D. String interpolation syntax is incorrect.

Solution

1. Step 1: Check parameter order rules in Ruby

   Parameters with default values must be placed after parameters without defaults.

2. Step 2: Analyze given method signature

   Here, name has default, but age does not and comes after. This causes syntax error.

3. Final Answer:

   Default parameters must come after non-default parameters. -> Option C

4. Quick Check:

   Default params after required params [OK]

Hint: Put default params after required ones [OK]

Common Mistakes:

• Placing default parameters before required ones
• Assuming return statement is mandatory
• Misreading string interpolation syntax

5. You want to define a method order that takes a product name and an optional quantity with default 1. Which is the best way to define it to allow calling order("apple") and order("apple", 5)?

hard

A. def order(product = "apple", quantity); "Order #{quantity} #{product}(s)"; end

B. def order(product, quantity = 1); "Order #{quantity} #{product}(s)"; end

C. def order(quantity = 1, product); "Order #{quantity} #{product}(s)"; end

D. def order(product, quantity); quantity ||= 1; "Order #{quantity} #{product}(s)"; end

Solution

1. Step 1: Identify correct parameter order and defaults

   Required parameters come first, then optional with default values.

2. Step 2: Evaluate each option

   def order(product, quantity = 1); "Order #{quantity} #{product}(s)"; end correctly places product first and quantity with default 1 second. def order(product = "apple", quantity); "Order #{quantity} #{product}(s)"; end has default before required, invalid. def order(quantity = 1, product); "Order #{quantity} #{product}(s)"; end swaps order incorrectly. def order(product, quantity); quantity ||= 1; "Order #{quantity} #{product}(s)"; end assigns default inside method but requires both arguments.

3. Final Answer:

   def order(product, quantity = 1); "Order #{quantity} #{product}(s)"; end -> Option B

4. Quick Check:

   Required first, default second = def order(product, quantity = 1); "Order #{quantity} #{product}(s)"; end [OK]

Hint: Put required params first, defaults after [OK]

Common Mistakes:

• Placing default parameter before required
• Assigning default inside method body instead of parameter list
• Confusing parameter order