Method declaration with def in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple method call

What is the output of this Ruby code?

Ruby

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

puts greet("Alice")

A greet

B Hello, Alice!

C Hello, name!

D nil

💡 Hint

Look at how the method uses string interpolation with the parameter.

The method greet takes a name and returns a greeting string with that name inserted. Calling puts on the method call prints the greeting.

❓ Predict Output

intermediate

Return value of method without explicit return

What does this Ruby method return when called with argument 5?

Ruby

def square(x)
  x * x
end

result = square(5)
puts result

A SyntaxError

B 5

C nil

D 25

💡 Hint

In Ruby, the last evaluated expression is returned by default.

The method multiplies x by itself and returns the result. Calling square(5) returns 25.

🔧 Debug

advanced

Identify the error in method declaration

What error does this Ruby code produce?

Ruby

def add_numbers(a, b)
  sum = a + b
  puts sum
end

add_numbers(3, 4)

A No error, outputs 7

B NoMethodError: undefined method 'add_numbers'

C TypeError: no implicit conversion of nil into Integer

D SyntaxError: unexpected end-of-input, expecting keyword_end

💡 Hint

Check if all method definitions are properly closed.

The method is missing the 'end' keyword to close the definition, causing a syntax error.

❓ Predict Output

advanced

Method with default parameter value

What is the output of this Ruby code?

Ruby

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

puts greet
puts greet("Bob")

A

Welcome, Guest!
Welcome, Bob!

B

Welcome, !
Welcome, Bob!

C

Welcome, Guest!
Welcome, Guest!

D SyntaxError

💡 Hint

Look at the default value assigned to the parameter.

If no argument is given, the method uses the default 'Guest'. Otherwise, it uses the provided name.

🧠 Conceptual

expert

Understanding method scope and variable visibility

Consider this Ruby code. What is the output?

Ruby

def change_var(x)
  x = 10
end

value = 5
change_var(value)
puts value

A nil

B 10

C 5

D NameError

💡 Hint

Think about whether the method changes the original variable or just a copy.

The method changes only the local copy of x, not the original variable 'value'. So 'value' remains 5.

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