Accessing and setting values in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to access the value of key 'name' in the hash.

Ruby

person = {"name" => "Alice", "age" => 30}
puts person[[1]]

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

A"name"

B:name

C"age"

D:age

Attempts:

3 left

💡 Hint

Common Mistakes

Using symbol keys like :name when the hash uses string keys.

Using the wrong key like "age" instead of "name".

In Ruby, to access a value in a hash with string keys, you use the string key inside brackets.

2fill in blank

medium

Complete the code to set the value of key :age to 25 in the hash.

Ruby

person = {name: "Bob", age: 20}
person[[1]] = 25
puts person[:age]

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

A"age"

B:age

C"name"

D:name

Attempts:

3 left

💡 Hint

Common Mistakes

Using string keys like "age" when the hash uses symbols.

Trying to set the value with the wrong key.

When the hash uses symbol keys, you must use the symbol to access or set values.

3fill in blank

hard

Fix the error in the code to correctly access the value of key :city.

Ruby

location = {city: "Paris", country: "France"}
puts location[[1]]

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

A"city"

B:country

C"country"

D:city

Attempts:

3 left

💡 Hint

Common Mistakes

Using string keys like "city" instead of symbol keys.

Using the wrong key like :country.

The hash uses symbol keys, so you must use :city to access the value.

4fill in blank

hard

Fill both blanks to create a hash with keys as strings and values as integers.

Ruby

scores = {"math" => [1], "science" => [2]
puts scores

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

A90

B"90"

C85

D"85"

Attempts:

3 left

💡 Hint

Common Mistakes

Using string values like "90" instead of integer 90.

Mixing string and integer types for values.

The keys are strings, so the values should be integers without quotes to represent numbers.

5fill in blank

hard

Fill all three blanks to create a hash with symbol keys and update one value.

Ruby

person = {name: [1], age: [2], city: [3]
person[:age] = 40
puts person

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

A"John"

B30

C"New York"

D"30"

Attempts:

3 left

💡 Hint

Common Mistakes

Using string "30" instead of integer 30 for age.

Not using quotes for string values.

Symbol keys are used with values: a string for name and city, and an integer for age. The age is updated later.

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