Instance methods in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of calling an instance method

What is the output of this Ruby code when calling the greet method on an instance of the Person class?

Ruby

class Person
  def initialize(name)
    @name = name
  end

  def greet
    "Hello, #{@name}!"
  end
end

person = Person.new("Alice")
puts person.greet

A Hello, Alice!

B Hello, @name!

C person.greet

D Error: undefined method greet

💡 Hint

Instance methods can access instance variables using @variable_name.

The greet method returns a string that includes the instance variable @name. Since person was initialized with "Alice", the output is "Hello, Alice!".

❓ Predict Output

intermediate

Instance method modifying state

What will be the output after running this Ruby code?

Ruby

class Counter
  def initialize
    @count = 0
  end

  def increment
    @count += 1
  end

  def current
    @count
  end
end

counter = Counter.new
counter.increment
counter.increment
puts counter.current

A 2

B 0

C 1

D Error: undefined method current

💡 Hint

Each call to increment adds 1 to @count.

The increment method adds 1 to the instance variable @count. After calling it twice, @count is 2, so current returns 2.

🔧 Debug

advanced

Why does this instance method raise an error?

This Ruby code raises an error when calling display. What is the cause?

Ruby

class Book
  def initialize(title)
    title = title
  end

  def display
    puts "Title: #{title}"
  end
end

book = Book.new("Ruby Guide")
book.display

A Missing return statement in initialize method

B Syntax error in initialize method

C Undefined local variable or method `title` in display method

D Cannot call puts inside instance method

💡 Hint

Instance variables start with @ and are needed to keep data between methods.

Inside initialize, title = title assigns the parameter to a local variable, not an instance variable. The display method tries to use title which is undefined in that scope, causing an error.

📝 Syntax

advanced

Identify the syntax error in this instance method

Which option correctly identifies the syntax error in this Ruby code?

Ruby

class Calculator
  def add(a, b)
    return a + b
  end

  def multiply(a, b)
    a * b
  # missing end here
end

calc = Calculator.new
puts calc.add(2, 3)

A Missing parentheses in method call add(2, 3)

B Missing <code>end</code> keyword for multiply method

C Incorrect use of return in add method

D Cannot create instance of Calculator without arguments

💡 Hint

Every method definition must be closed with end.

The multiply method is missing its closing end, causing a syntax error.

🚀 Application

expert

How many times is the instance method called?

Consider this Ruby code. How many times is the log instance method called during execution?

Ruby

class Logger
  def initialize
    @count = 0
  end

  def log(message)
    @count += 1
    puts "Log ##{@count}: #{message}"
  end

  def repeat_log(times, message)
    times.times { log(message) }
  end
end

logger = Logger.new
logger.log("Start")
logger.repeat_log(3, "Repeat")
logger.log("End")

A 6

B 4

C 3

D 5

💡 Hint

Count each explicit call to log, including inside loops.

The log method is called once before repeat_log, then 3 times inside repeat_log, and once more after. Total calls: 1 + 3 + 1 = 5.