Method declaration with def in Ruby - Mini Project: Build & Apply

Method declaration with def in Ruby

📖 Scenario: You are creating a simple calculator program that can add two numbers.

🎯 Goal: Build a Ruby method that takes two numbers and returns their sum.

📋 What You'll Learn

Create a method named add_numbers that takes two parameters: num1 and num2.

Inside the method, return the sum of num1 and num2.

Call the method with the numbers 5 and 7 and print the result.

💡 Why This Matters

🌍 Real World

Methods help organize code into reusable blocks, like a calculator that can add many pairs of numbers without rewriting code.

💼 Career

Knowing how to write methods is essential for any programming job, as it helps keep code clean and easy to maintain.

1

Create the method declaration

Write a method declaration named add_numbers that takes two parameters: num1 and num2. Do not add any code inside the method yet.

Ruby

def add_numbers(num1, num2)
  # Your code here
end

Hint

Use def to start the method and end to finish it.

2

Add the return statement inside the method

Inside the add_numbers method, write a line that returns the sum of num1 and num2.

Ruby

def add_numbers(num1, num2)
  # Your code here
end

Hint

Use return num1 + num2 to send back the sum.

3

Call the method with two numbers

Call the method add_numbers with the arguments 5 and 7, and save the result in a variable named result.

Ruby

def add_numbers(num1, num2)
  return num1 + num2
end

# Your code here

Hint

Use result = add_numbers(5, 7) to call the method and store the answer.

4

Print the result

Write a line to print the value of the variable result.

Ruby

def add_numbers(num1, num2)
  return num1 + num2
end

result = add_numbers(5, 7)
# Your code here

Hint

Use puts result to show the sum on the screen.

Practice

1. What keyword do you use in Ruby to start defining a method?

easy

A. method

B. function

C. define

D. def

Solution

1. Step 1: Understand Ruby method syntax

   In Ruby, methods start with the keyword def and end with end.

2. Step 2: Identify the correct keyword

   The correct keyword to start a method is def, not function, method, or define.

3. Final Answer:

   def -> Option D

4. Quick Check:

   Method start keyword = def [OK]

Hint: Remember: Ruby methods start with 'def' and end with 'end' [OK]

Common Mistakes:

• Using 'function' like in JavaScript
• Using 'method' keyword which doesn't exist
• Forgetting to use 'def' to start method

2. Which of the following is the correct way to declare a method named greet in Ruby?

easy

A. def greet puts "Hello"

B. function greet() { puts "Hello" }

C. def greet() puts "Hello" end

D. method greet() puts "Hello" end

Solution

1. Step 1: Check Ruby method syntax

   Ruby methods start with def method_name() and end with end. Parentheses are optional but allowed.

2. Step 2: Identify correct syntax

   def greet() puts "Hello" end uses def greet() puts "Hello" end, which is correct Ruby syntax. Options B and D use wrong keywords, and C misses end.

3. Final Answer:

   def greet() puts "Hello" end -> Option C

4. Quick Check:

   Correct Ruby method syntax = def greet() puts "Hello" end [OK]

Hint: Use 'def name() ... end' to declare methods in Ruby [OK]

Common Mistakes:

• Forgetting the 'end' keyword
• Using JavaScript style 'function' keyword
• Missing parentheses or using wrong keywords

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

def add(a, b)
  a + b
end

puts add(3, 4)

medium

A. 7

B. 34

C. a + b

D. Error

Solution

1. Step 1: Understand method parameters and return

   The method add takes two parameters a and b and returns their sum a + b.

2. Step 2: Calculate the method call result

   Calling add(3, 4) returns 3 + 4 = 7, which is printed by puts.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Method returns last expression value; 3 + 4 = 7 [OK]

Common Mistakes:

• Thinking it concatenates as strings
• Expecting explicit return keyword
• Confusing output with code text

4. Identify the error in this Ruby method declaration:

def say_hello
  puts "Hello"

medium

A. Missing 'end' keyword to close method

B. Missing parentheses after method name

C. Incorrect use of puts inside method

D. Method name cannot have underscore

Solution

1. Step 1: Check method structure

   Ruby methods must start with def and end with end. This code misses the end keyword.

2. Step 2: Identify the missing part

   Without end, Ruby will raise a syntax error because the method is not properly closed.

3. Final Answer:

   Missing 'end' keyword to close method -> Option A

4. Quick Check:

   Every method needs 'end' [OK]

Hint: Always close methods with 'end' keyword [OK]

Common Mistakes:

• Forgetting 'end' after method body
• Thinking parentheses are mandatory
• Assuming underscores are invalid in names

5. You want to create a method greet_person that takes a name and returns a greeting like "Hello, Alice!". Which code correctly does this?

hard

A. def greet_person(name)
puts "Hello, #{name}!"
end

B. def greet_person(name)
"Hello, " + name + "!"
end

C. def greet_person(name)
return puts "Hello, " + name + "!"
end

D. def greet_person(name)
print "Hello, " + name + "!"
end

Solution

1. Step 1: Understand method return vs output

   To return a greeting string, the method should produce the string as its last expression or use return. Using puts or print outputs to console but returns nil.

2. Step 2: Analyze each option

   def greet_person(name) "Hello, " + name + "!" end returns the greeting string correctly. def greet_person(name) puts "Hello, #{name}!" end prints but returns nil. def greet_person(name) return puts "Hello, " + name + "!" end returns nil because puts returns nil. def greet_person(name) print "Hello, " + name + "!" end prints but does not return the string.

3. Final Answer:

   def greet_person(name) "Hello, " + name + "!" end -> Option B

4. Quick Check:

   Return string, not print it [OK]

Hint: Return string directly; puts prints but returns nil [OK]

Common Mistakes:

• Using puts instead of returning string
• Returning result of puts (which is nil)
• Confusing print with return