Accessing and setting values in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code?

Consider the following Ruby code snippet. What will be printed when it runs?

Ruby

hash = {a: 1, b: 2}
hash[:c] = 3
puts hash[:b]

A 2

B 3

C KeyError

D nil

💡 Hint

Look at how the hash is accessed and what key is used in puts.

The hash initially has keys :a and :b with values 1 and 2. We add :c with value 3. Then we print the value for key :b, which is 2.

❓ Predict Output

intermediate

What does this code output after setting a nested value?

Look at this Ruby code that sets a nested value in a hash. What will it print?

Ruby

data = {user: {name: "Alice", age: 30}}
data[:user][:age] = 31
puts data[:user][:age]

A 30

B NoMethodError

C nil

D 31

💡 Hint

Check how the nested hash value is updated before printing.

The nested hash under :user has :age initially 30. It is updated to 31, so printing it outputs 31.

❓ Predict Output

advanced

What is the output of this Ruby code?

Consider the following Ruby code snippet. What will be printed when it runs?

Ruby

hash = {a: 1, b: 2}
puts hash[:c].to_s.length

A 0

B TypeError

C NoMethodError

D 1

💡 Hint

Think about what happens when accessing a missing key in a hash and calling to_s on nil.

Accessing hash[:c] returns nil since :c is missing. Calling to_s on nil returns an empty string "". Its length is 0.

❓ Predict Output

advanced

What is the final value of the variable after setting values?

What will be the value of the variable 'arr' after running this Ruby code?

Ruby

arr = [1, 2, 3]
arr[1] = 5
arr[3] = 7
p arr

A [1, 5, 3]

B [1, 5, 3, 7]

C [1, 5, 7]

D [1, 2, 3, 7]

💡 Hint

Remember how Ruby arrays handle assignment beyond current length.

Assigning arr[1] = 5 changes second element to 5. Assigning arr[3] = 7 adds a new element at index 3. The array becomes [1, 5, 3, 7].

🧠 Conceptual

expert

Which option produces the exact output '42'?

Given the following Ruby code, which option will print exactly '42'?

Ruby

value = {x: 40}
# Your code here
puts value[:x]

A value[:x] = 42.to_s

B value[:x] = '42'

C value[:x] += 2

D value[:x] = 40 + '2'

💡 Hint

Consider the type of value[:x] and how to get the number 42 printed.

Option C adds 2 to the integer 40, resulting in 42. Printing value[:x] outputs 42. Option C sets it to string '42' but printing will output '42' as string, which looks the same but is not the integer 42. Option C converts 42 to string, also prints '42' as string. Option C causes a TypeError because you cannot add integer and string.

Practice

1. Which of the following correctly accesses the first element of an array arr in Ruby using indexing?

easy

A. arr[1]

B. arr.first()

C. arr[0]

D. arr.get(0)

Solution

1. Step 1: Understand array indexing in Ruby

   Ruby arrays start at index 0, so the first element is at arr[0].

2. Step 2: Check each option

   arr[0] correctly accesses the first element. arr[1] accesses the second element. arr.first() is a method call that also returns the first element but is not using square brackets. arr.get(0) is invalid syntax in Ruby.

3. Final Answer:

   arr[0] -> Option C

4. Quick Check:

   First element index = 0 [OK]

Hint: Remember: array indexes start at zero in Ruby [OK]

Common Mistakes:

• Using index 1 for first element
• Using method calls instead of brackets
• Trying to use non-existent methods like get()

2. Which syntax correctly sets the value of key :name to "Alice" in a Ruby hash person?

easy

A. person[:name] == "Alice"

B. person.name = "Alice"

C. person["name"] = Alice

D. person[:name] = "Alice"

Solution

1. Step 1: Understand hash key assignment syntax

   To set a value in a hash, use square brackets with the key and assign with =.

2. Step 2: Analyze each option

   person[:name] = "Alice" correctly sets the key :name. person.name = "Alice" is invalid for hashes. person["name"] = Alice misses quotes around Alice, causing error. person[:name] == "Alice" is a comparison, not assignment.

3. Final Answer:

   person[:name] = "Alice" -> Option D

4. Quick Check:

   Use brackets and = for hash assignment [OK]

Hint: Use brackets and = to set hash values [OK]

Common Mistakes:

• Using dot notation for hashes
• Forgetting quotes around string values
• Using == instead of = for assignment

3. What is the output of the following Ruby code?

arr = [10, 20, 30]
arr[1] = 50
puts arr.inspect

medium

A. [10, 50, 30]

B. [10, 20, 30]

C. [50, 20, 30]

D. Error

Solution

1. Step 1: Understand array element assignment

   Assigning arr[1] = 50 changes the element at index 1 (second element) to 50.

2. Step 2: Check the array after assignment

   Original array is [10, 20, 30]. After assignment, it becomes [10, 50, 30].

3. Final Answer:

   [10, 50, 30] -> Option A

4. Quick Check:

   Index 1 value changed to 50 [OK]

Hint: Index 1 means second element in array [OK]

Common Mistakes:

• Thinking index 1 is first element
• Expecting original array unchanged
• Confusing assignment with comparison

4. Identify the error in this Ruby code that tries to set a hash value:

person = {name: "Bob"}
person.name = "Charlie"

medium

A. Missing quotes around "Charlie"

B. Using dot notation to set hash value causes error

C. Hash keys must be strings, not symbols

D. person variable is not defined

Solution

1. Step 1: Understand hash value setting syntax

   Hashes use square brackets with keys to access or set values, not dot notation.

2. Step 2: Analyze the code

   person.name = "Charlie" tries to use dot notation, which is invalid for hashes and causes an error.

3. Final Answer:

   Using dot notation to set hash value causes error -> Option B

4. Quick Check:

   Use brackets, not dot, for hash assignment [OK]

Hint: Use brackets, not dot, to set hash values [OK]

Common Mistakes:

• Using dot notation for hashes
• Confusing symbols and strings for keys
• Assuming variable is undefined

5. Given the nested hash data = {user: {name: "Eve", age: 28}}, how do you change the user's age to 30?

hard

A. data[:user][:age] = 30

B. data[:user.age] = 30

C. data.user[:age] = 30

D. data[:user][age] = 30

Solution

1. Step 1: Access nested hash keys with brackets

   To access nested values, use square brackets for each key: data[:user][:age].

2. Step 2: Assign new value to nested key

   Set data[:user][:age] = 30 to update the age.

3. Final Answer:

   data[:user][:age] = 30 -> Option A

4. Quick Check:

   Use chained brackets for nested hashes [OK]

Hint: Chain brackets for nested hash keys [OK]

Common Mistakes:

• Using dot notation for hashes
• Missing quotes or symbols for keys
• Using undefined variables as keys