Why arrays are fundamental in Ruby - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an empty array in Ruby.

Ruby

my_array = [1]

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

A{}

B[]

C()

D<>

Attempts:

3 left

💡 Hint

Common Mistakes

Using curly braces {} which create a hash, not an array.

Using parentheses () which are for method calls or grouping.

In Ruby, arrays are created using square brackets [].

2fill in blank

medium

Complete the code to add the number 5 to the end of the array.

Ruby

numbers = [1, 2, 3]
numbers.[1](5)
puts numbers.inspect

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

Apush

Bpop

Cshift

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop which removes the last element.

Using shift which removes the first element.

The push method adds an element to the end of an array.

3fill in blank

hard

Fix the error in the code to access the first element of the array.

Ruby

fruits = ['apple', 'banana', 'cherry']
first = fruits[1]
puts first

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

A[0]

B(0)

C(1)

D{0}

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of square brackets.

Using curly braces which are for hashes.

Arrays in Ruby use square brackets with zero-based indexes to access elements.

4fill in blank

hard

Fill both blanks to create an array of squares for numbers 1 to 5.

Ruby

squares = (1..5).[1] { |n| n [2] n }
puts squares.inspect

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

Amap

B*

C+

Dselect

Attempts:

3 left

💡 Hint

Common Mistakes

Using select which filters elements instead of transforming.

Using + which adds numbers instead of multiplying.

The map method transforms each number by multiplying it by itself.

5fill in blank

hard

Fill all three blanks to select even numbers and double them.

Ruby

result = (1..10).[1] { |x| x [2] 2 == 0 }.[3] { |x| x * 2 }
puts result.inspect

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

Amap

B%

Cselect

Dfilter

Attempts:

3 left

💡 Hint

Common Mistakes

Using filter which is not a Ruby array method.

Using + instead of % to check evenness.

First, select filters even numbers using the modulo operator %, then map doubles each selected number.

Practice

1. Why are arrays considered fundamental in Ruby programming?

easy

A. Because they are used to write text files

B. Because they store multiple items in an ordered list

C. Because they cannot be changed once created

D. Because they only store numbers

Solution

1. Step 1: Understand what arrays do

   Arrays hold many items together in a specific order, making it easy to manage groups of data.

2. Step 2: Compare options with array features

   Only Because they store multiple items in an ordered list correctly describes arrays as ordered collections of multiple items.

3. Final Answer:

   Because they store multiple items in an ordered list -> Option B

4. Quick Check:

   Arrays = ordered collections [OK]

Hint: Arrays hold many items in order, like a list [OK]

Common Mistakes:

• Thinking arrays only hold numbers
• Believing arrays are immutable
• Confusing arrays with file operations

2. Which of the following is the correct way to create an array in Ruby?

easy

A. array = [1, 2, 3]

B. array = (1, 2, 3)

C. array = {1, 2, 3}

D. array = <1, 2, 3>

Solution

1. Step 1: Recall Ruby array syntax

   Arrays in Ruby are created using square brackets [] with items separated by commas.

2. Step 2: Check each option's syntax

   Only array = [1, 2, 3] uses square brackets correctly; others use parentheses, braces, or angle brackets which are invalid for arrays.

3. Final Answer:

   array = [1, 2, 3] -> Option A

4. Quick Check:

   Arrays use [] brackets [OK]

Hint: Use square brackets [] to create arrays [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Confusing arrays with hashes (curly braces)
• Using angle brackets which are invalid

3. What is the output of this Ruby code?

arr = [10, 20, 30]
puts arr[1]

medium

A. 20

B. 10

C. 30

D. nil

Solution

1. Step 1: Understand array indexing in Ruby

   Ruby arrays start at index 0, so arr[0] is 10, arr[1] is 20, arr[2] is 30.

2. Step 2: Identify the value at index 1

   The code prints arr[1], which is 20.

3. Final Answer:

   20 -> Option A

4. Quick Check:

   arr[1] = 20 [OK]

Hint: Remember Ruby arrays start at index 0 [OK]

Common Mistakes:

• Thinking array index starts at 1
• Confusing values at different indexes
• Expecting nil for valid index

4. Identify the error in this Ruby code that tries to add an item to an array:

numbers = [1, 2, 3]
numbers.add(4)

medium

A. The syntax for array creation is wrong

B. The array is immutable and cannot be changed

C. The method 'add' does not exist for arrays

D. The number 4 must be inside quotes

Solution

1. Step 1: Check the method used to add items to arrays

   Ruby arrays use 'push' or '<<' to add items, not 'add'.

2. Step 2: Identify the error cause

   Calling 'add' on an array causes a NoMethodError because it is not a valid method.

3. Final Answer:

   The method 'add' does not exist for arrays -> Option C

4. Quick Check:

   Use 'push' or '<<' to add items [OK]

Hint: Use 'push' or '<<' to add items to arrays [OK]

Common Mistakes:

• Using 'add' instead of 'push' or '<<'
• Thinking arrays cannot be changed
• Adding numbers as strings unnecessarily

5. Given an array arr = [1, 2, 3, 4, 5], which Ruby code correctly creates a new array with only even numbers?

hard

A. new_arr = arr.map { |num| num * 2 }

B. new_arr = arr.push(2, 4)

C. new_arr = arr.delete_if { |num| num.even? }

D. new_arr = arr.select { |num| num % 2 == 0 }

Solution

1. Step 1: Understand the goal

   We want a new array containing only even numbers from the original array.

2. Step 2: Analyze each option

   new_arr = arr.select { |num| num % 2 == 0 } uses 'select' to filter even numbers correctly. new_arr = arr.map { |num| num * 2 } doubles all numbers, not filtering. new_arr = arr.delete_if { |num| num.even? } deletes even numbers, opposite of goal. new_arr = arr.push(2, 4) adds 2 and 4 to original array, not filtering.

3. Final Answer:

   new_arr = arr.select { |num| num % 2 == 0 } -> Option D

4. Quick Check:

   Use 'select' to filter arrays [OK]

Hint: Use 'select' to pick items matching a condition [OK]

Common Mistakes:

• Using 'map' instead of 'select' for filtering
• Deleting instead of selecting items
• Adding items instead of filtering