Parameters with default values in Ruby - Mini Project: Build & Apply

Parameters with default values

📖 Scenario: You are creating a simple greeting system for a website. Sometimes users provide their name, and sometimes they don't. You want to write a method that can greet users by name if given, or greet them with a generic message if no name is provided.

🎯 Goal: Build a Ruby method called greet that takes one parameter name with a default value. The method should return a greeting message using the given name or a default greeting if no name is given.

📋 What You'll Learn

Create a method called greet with one parameter name that has a default value of "Guest".

Inside the method, return a string that says "Hello, <name>!" where <name> is the parameter value.

Call the greet method twice: once without any argument, and once with the argument "Alice".

Print the results of both method calls.

💡 Why This Matters

🌍 Real World

Default parameters are useful when you want to make your methods flexible and easy to use without always requiring all information.

💼 Career

Understanding default parameters helps you write cleaner, more maintainable code in Ruby, which is important for many programming jobs.

1

Create the greet method with a name parameter

Write a method called greet that takes one parameter named name. Do not add a default value yet.

Ruby

def greet(name)
  # Your code here
end

Hint

Use def to define the method and include name inside parentheses.

2

Add a default value "Guest" to the name parameter

Modify the greet method so that the parameter name has a default value of "Guest".

Ruby

def greet(name = "Guest")
  # Your code here
end

Hint

Set the default value by writing name = "Guest" inside the parentheses.

3

Return a greeting message using the name parameter

Inside the greet method, return a string that says "Hello, <name>!" where <name> is the value of the name parameter. Use string interpolation.

Ruby

def greet(name = "Guest")
  # Your code here
end

Hint

Use "Hello, #{name}!" to create the greeting string.

4

Call greet with and without an argument and print the results

Call the greet method twice: once without any argument, and once with the argument "Alice". Print both results using puts.

Ruby

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

# Your code here

Hint

Use puts greet and puts greet("Alice") to print the greetings.

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