Accessing elements (indexing, first, last) in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of accessing the first and last elements?

Consider the Ruby array arr = [10, 20, 30, 40, 50]. What will be printed by the following code?

puts arr.first
puts arr.last

Ruby

arr = [10, 20, 30, 40, 50]
puts arr.first
puts arr.last

A 10\n10

B 50\n10

C 10\n50

D 50\n50

💡 Hint

Remember, first gives the first element and last gives the last element of an array.

The first method returns the first element (10), and last returns the last element (50). So the output is 10 then 50 on separate lines.

❓ Predict Output

intermediate

What is the output of negative indexing in Ruby arrays?

Given the array nums = [5, 10, 15, 20, 25], what will puts nums[-2] print?

Ruby

nums = [5, 10, 15, 20, 25]
puts nums[-2]

A 15

B 20

C 25

D 10

💡 Hint

Negative indices count from the end of the array, starting at -1 for the last element.

Index -1 is the last element (25), so -2 is the second last element (20).

❓ Predict Output

advanced

What happens when accessing an out-of-range index?

What will the following Ruby code print?

arr = [1, 2, 3]
puts arr[5].inspect

Ruby

arr = [1, 2, 3]
puts arr[5].inspect

A nil

B IndexError

C 3

D 0

💡 Hint

Ruby returns nil when you access an index outside the array bounds.

Accessing an index beyond the array length returns nil instead of an error.

❓ Predict Output

advanced

What is the output when using first(n) and last(n) methods?

Given arr = [7, 14, 21, 28, 35], what will the following code print?

p arr.first(3)
p arr.last(2)

Ruby

arr = [7, 14, 21, 28, 35]
p arr.first(3)
p arr.last(2)

A [7, 14]\n[28, 35]

B [7, 14, 21]\n[21, 28]

C [14, 21, 28]\n[28, 35]

D [7, 14, 21]\n[28, 35]

💡 Hint

The first(n) method returns the first n elements, and last(n) returns the last n elements.

The first 3 elements are [7, 14, 21], and the last 2 elements are [28, 35].

🧠 Conceptual

expert

What is the value of result after this code runs?

Consider this Ruby code:

arr = ['a', 'b', 'c', 'd']
result = arr[-1] + arr[0] + arr[-3]

What is the value of result?

Ruby

arr = ['a', 'b', 'c', 'd']
result = arr[-1] + arr[0] + arr[-3]

A "dab"

B "d a b"

C "dcb"

D "dac"

💡 Hint

Remember that negative indices count from the end: -1 is last, -2 is second last, etc.

arr[-1] is 'd', arr[0] is 'a', arr[-3] is 'b'. Concatenating gives 'd' + 'a' + 'b' = "dab".