Each as the primary iterator in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of each with array iteration

What is the output of this Ruby code?

Ruby

arr = [1, 2, 3]
result = []
arr.each do |x|
  result << x * 2
end
puts result.inspect

A [2, 4, 6]

B [1, 2, 3]

C nil

D [3, 6, 9]

💡 Hint

Remember that each goes through every element and you can collect results in another array.

The each method goes through each element in arr. For each element x, it multiplies by 2 and adds to result. So result becomes [2, 4, 6].

❓ Predict Output

intermediate

Each with hash iteration output

What will this Ruby code print?

Ruby

h = {a: 1, b: 2}
h.each do |key, value|
  puts "#{key}:#{value * 3}"
end

A

a:3
b:2

B

a:1
b:2

C

a:1
b:6

D

a:3
b:6

💡 Hint

Each goes through each key-value pair. Value is multiplied by 3 in the output.

The each method iterates over each key-value pair. For each, it prints key and value multiplied by 3. So a:3 and b:6 are printed.

🔧 Debug

advanced

Why does this each loop not modify the array?

Look at this Ruby code. Why does the array stay the same after the each loop?

Ruby

arr = [1, 2, 3]
arr.each do |x|
  x = x * 10
end
puts arr.inspect

A Because x is a copy of each element, modifying x does not change the array elements.

B Because each does not run the block at all.

C Because x is a reference to the array element and changes should reflect.

D Because the array is frozen and cannot be changed.

💡 Hint

Think about whether changing the block variable changes the original array element.

In Ruby, the block variable x is a copy of the element's value. Assigning x = x * 10 changes only x, not the original array element. So arr stays [1, 2, 3].

📝 Syntax

advanced

Identify the syntax error in this each block

Which option shows the correct way to write this each block without syntax errors?

Ruby

arr = [1, 2, 3]
arr.each do |x|
  puts x

A

arr.each |x| do
  puts x
end

B

arr.each do |x|
  puts x
end

C

arr.each do |x|
  puts x

D

arr.each do x |
  puts x
end

💡 Hint

Remember the syntax for blocks with do...end and pipes for block variables.

Option B correctly uses do |x| ... end. Option B has wrong order of pipes and do. Option B misses end. Option B has misplaced pipe.

🚀 Application

expert

Count how many elements are even using each

Using each as the primary iterator, what is the value of count after running this code?

Ruby

arr = [4, 7, 10, 3, 6]
count = 0
arr.each do |num|
  count += 1 if num.even?
end
puts count

A 4

B 2

C 3

D 5

💡 Hint

Check which numbers in the array are even and count them.

The even numbers are 4, 10, and 6. So count increases 3 times. The final count is 3.

Practice

1. What does the each method do in Ruby when used on an array?

easy

A. It returns a new array with modified items.

B. It runs a block of code once for every item in the array.

C. It changes the array by removing items.

D. It sorts the array in ascending order.

Solution

1. Step 1: Understand the purpose of each

   The each method is used to run a block of code for every item in a collection like an array.

2. Step 2: Check what each does to the array

   It does not change or sort the array; it simply processes each item one by one.

3. Final Answer:

   It runs a block of code once for every item in the array. -> Option B

4. Quick Check:

   each runs code on each item [OK]

Hint: Remember: each processes items, does not change array [OK]

Common Mistakes:

• Thinking each modifies the array
• Confusing each with methods like map
• Assuming each returns a new array

2. Which of the following is the correct syntax to use each on an array numbers to print each number?

easy

A. each numbers { |num| puts num }

B. numbers.each do num puts num end

C. numbers.each { |num| puts num }

D. numbers.each |num| puts num

Solution

1. Step 1: Identify correct block syntax with each

   The correct syntax uses each followed by a block with { |variable| ... } or do |variable| ... end.

2. Step 2: Check each option

   numbers.each { |num| puts num } uses numbers.each { |num| puts num } which is correct. Others have syntax errors or wrong order.

3. Final Answer:

   numbers.each { |num| puts num } -> Option C

4. Quick Check:

   Correct block syntax = numbers.each { |num| puts num } [OK]

Hint: Use each { |item| ... } or each do |item| ... end [OK]

Common Mistakes:

• Writing each numbers instead of numbers.each
• Missing block delimiters like braces or do-end
• Not using pipes | | around block variable

3. What is the output of this Ruby code?

fruits = ['apple', 'banana', 'cherry']
fruits.each { |fruit| puts fruit.upcase }

medium

A. APPLE
BANANA
CHERRY

B. apple
banana
cherry

C. ['APPLE', 'BANANA', 'CHERRY']

D. Error: undefined method upcase for fruit

Solution

1. Step 1: Understand what each does with puts fruit.upcase

   The each method runs the block for each fruit, printing the uppercase version.

2. Step 2: Check output line by line

   It prints 'APPLE', then 'BANANA', then 'CHERRY' each on a new line.

3. Final Answer:

   APPLE BANANA CHERRY -> Option A

4. Quick Check:

   each prints uppercase fruits [OK]

Hint: Remember puts prints each item on a new line [OK]

Common Mistakes:

• Thinking each returns a new array
• Expecting lowercase output
• Confusing puts with returning a list

4. What is wrong with this Ruby code snippet?

items = [1, 2, 3]
items.each do item
  puts item * 2
end

medium

A. Array items is empty

B. Using do instead of braces is invalid

C. Cannot multiply numbers inside each

D. Missing pipes around block variable: should be |item|

Solution

1. Step 1: Check block variable syntax in each do block

   When using do with each, the block variable must be inside pipes: do |item|.

2. Step 2: Identify the error

   The code misses pipes around item, causing a syntax error.

3. Final Answer:

   Missing pipes around block variable: should be |item| -> Option D

4. Quick Check:

   Block variables need pipes | | [OK]

Hint: Always put block variables inside | | with each do [OK]

Common Mistakes:

• Omitting pipes around block variables
• Thinking do is invalid with each
• Assuming multiplication inside each is wrong

5. Given a hash scores = { alice: 10, bob: 15, carol: 12 }, how can you use each to print each name and score in the format Name: Score?

hard

A. scores.each { |name, score| puts "#{name.capitalize}: #{score}" }

B. scores.each { |score, name| puts "#{name}: #{score}" }

C. scores.each { |name| puts "#{name}: #{score}" }

D. scores.each { |name, score| puts "#{score.capitalize}: #{name}" }

Solution

1. Step 1: Understand each on a hash

   When using each on a hash, the block receives two variables: key and value.

2. Step 2: Match variables and format output

   The key is the name (symbol), value is the score. Use name.capitalize to print the name nicely.

3. Final Answer:

   scores.each { |name, score| puts "#{name.capitalize}: #{score}" } -> Option A

4. Quick Check:

   Hash each uses key, value pairs [OK]

Hint: Hash each block gets two vars: key and value [OK]

Common Mistakes:

• Swapping key and value variables
• Using only one block variable for hash
• Trying to capitalize a number