Instance variables (@) in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an instance variable in the initialize method.

Ruby

class Person
  def initialize(name)
    [1] = name
  end
end

Drag options to blanks, or click blank then click option'

A@name

Bname

C$name

Dself.name

Attempts:

3 left

💡 Hint

Common Mistakes

Using a local variable instead of an instance variable.

Using global variable syntax ($) instead of instance variable (@).

The @ symbol is used to define instance variables in Ruby. Here, @name stores the value for each object.

2fill in blank

medium

Complete the code to access the instance variable inside a method.

Ruby

class Car
  def initialize(model)
    @model = model
  end

  def show_model
    puts [1]
  end
end

Drag options to blanks, or click blank then click option'

Amodel

Bself.model

C@model

D$model

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access the variable without @.

Using global variable syntax ($) instead of instance variable (@).

To access an instance variable inside a method, use the @ symbol before the variable name.

3fill in blank

hard

Fix the error in the code by completing the instance variable assignment.

Ruby

class Book
  def initialize(title)
    [1] = title
  end

  def title
    @title
  end
end

Drag options to blanks, or click blank then click option'

A@title

Btitle

C$title

Dself.title

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning to a local variable instead of an instance variable.

Using global variable syntax ($) instead of instance variable (@).

The instance variable must be assigned with @title to be accessible in other methods.

4fill in blank

hard

Fill both blanks to create a method that updates and returns an instance variable.

Ruby

class User
  def initialize(age)
    @age = age
  end

  def birthday
    @age [1] 1
    return [2]
  end
end

Drag options to blanks, or click blank then click option'

A+=

B-=

C@age

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using -= instead of +=.

Returning a local variable instead of the instance variable.

The += operator adds 1 to the instance variable @age. Then returning @age shows the updated value.

5fill in blank

hard

Fill all three blanks to define an instance variable, update it, and return it.

Ruby

class Counter
  def initialize(start)
    [1] = start
  end

  def increment
    [2] [3] 1
    return @count
  end
end

Drag options to blanks, or click blank then click option'

A@count

B+=

C-=

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning to a local variable instead of an instance variable.

Using -= instead of +=.

Trying to update a variable without @.

Instance variable @count is assigned in initialize, incremented with +=, and returned.

Practice

1. What does an instance variable in Ruby always start with?

easy

A. An at symbol (@)

B. A dollar sign ($)

C. A hash symbol (#)

D. A percent sign (%)

Solution

1. Step 1: Recall Ruby instance variable syntax

   Instance variables in Ruby always begin with the at symbol (@) to distinguish them from local variables.

2. Step 2: Identify the correct symbol

   Among the options, only the at symbol (@) is used to start instance variables.

3. Final Answer:

   An at symbol (@) -> Option A

4. Quick Check:

   Instance variable starts with @ [OK]

Hint: Instance variables always start with @ in Ruby [OK]

Common Mistakes:

• Confusing instance variables with global variables ($)
• Using local variable syntax without @
• Thinking instance variables start with # or %

2. Which of the following is the correct way to define an instance variable inside a Ruby class?

easy

A. var @name = 'Alice'

B. @name = 'Alice'

C. name = @'Alice'

D. def @name = 'Alice'

Solution

1. Step 1: Understand instance variable assignment syntax

   In Ruby, instance variables are assigned by writing @variable_name = value inside methods or constructors.

2. Step 2: Check each option

   @name = 'Alice' correctly assigns an instance variable. The other options use invalid syntax.

3. Final Answer:

   @name = 'Alice' -> Option B

4. Quick Check:

   Assign instance variable with @name = value [OK]

Hint: Assign instance variables with @name = value inside methods [OK]

Common Mistakes:

• Adding var keyword (not used in Ruby)
• Placing @ inside quotes
• Using def keyword incorrectly

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

class Person
  def initialize(name)
    @name = name
  end
  def greet
    "Hello, #{@name}!"
  end
end

p = Person.new('Bob')
puts p.greet

medium

A. Error: undefined variable

B. Hello, @name!

C. Hello, name!

D. Hello, Bob!

Solution

1. Step 1: Understand instance variable assignment in initialize

   The initialize method sets @name to 'Bob' when Person.new('Bob') is called.

2. Step 2: Evaluate greet method output

   The greet method returns a string with #{@name} replaced by the instance variable value 'Bob'.

3. Final Answer:

   Hello, Bob! -> Option D

4. Quick Check:

   Instance variable @name holds 'Bob' so output is Hello, Bob! [OK]

Hint: Instance variables keep data per object, used inside methods with @ [OK]

Common Mistakes:

• Expecting literal '@name' in output
• Confusing local and instance variables
• Forgetting to use @ in string interpolation

4. Identify the error in this Ruby class code:

class Car
  def initialize(model)
    name = model
  end
  def show
    puts @name
  end
end

car = Car.new('Tesla')
car.show

medium

A. Syntax error in initialize method

B. Method show is missing return statement

C. Instance variable @name is not assigned, so nil is printed

D. Cannot call puts inside method

Solution

1. Step 1: Check variable assignment in initialize

   The code assigns local variable name = model, not instance variable @name.

2. Step 2: Understand effect on show method

   Since @name is never set, @name is nil, so puts prints an empty line (nil).

3. Final Answer:

   Instance variable @name is not assigned, so nil is printed -> Option C

4. Quick Check:

   Local variable assigned, not instance variable @name [OK]

Hint: Use @ to assign instance variables, not plain variable names [OK]

Common Mistakes:

• Assigning local variable instead of instance variable
• Expecting puts to fail without return
• Thinking syntax error occurs here

5. You want to create a Ruby class Book that stores a title and author as instance variables. You also want a method description that returns "Title by Author". Which code correctly implements this?

hard

A. class Book
def initialize(title, author)
@title = title
@author = author
end
def description
"#{@title} by #{@author}"
end
end

B. class Book
def initialize(title, author)
title = @title
author = @author
end
def description
"#{title} by #{author}"
end
end

C. class Book
def initialize(title, author)
@title = title
@author = author
end
def description
"title by author"
end
end

D. class Book
def initialize(title, author)
@title = title
@author = author
end
def description
"#{title} by #{author}"
end
end

Solution

1. Step 1: Assign instance variables correctly in initialize

   class Book def initialize(title, author) @title = title @author = author end def description "#{@title} by #{@author}" end end assigns @title and @author from parameters correctly. class Book def initialize(title, author) title = @title author = @author end def description "#{title} by #{author}" end end reverses assignment. The remaining options misuse variables in description.

2. Step 2: Use instance variables in description method

   class Book def initialize(title, author) @title = title @author = author end def description "#{@title} by #{@author}" end end uses #{@title} and #{@author} inside string interpolation, correctly accessing instance variables.

3. Final Answer:

   class Book def initialize(title, author) @title = title @author = author end def description "#{@title} by #{@author}" end end -> Option A

4. Quick Check:

   Assign and use @variables inside methods for correct output [OK]

Hint: Assign and use instance variables with @ inside all methods [OK]

Common Mistakes:

• Assigning variables backwards (param = @var)
• Using local variables instead of instance variables in methods
• Returning literal strings without interpolation