Array iteration and enumerated in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print each element in the array.

Swift

let fruits = ["Apple", "Banana", "Cherry"]
for fruit in [1] {
    print(fruit)
}

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

Afruits

Bfruit

Carray

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using the loop variable name instead of the array name.

Using a variable name that is not declared.

The loop iterates over the array named fruits. So, fruits is the correct variable to use.

2fill in blank

medium

Complete the code to print the index and value of each element using enumerated().

Swift

let colors = ["Red", "Green", "Blue"]
for (index, color) in colors.[1]() {
    print("\(index): \(color)")
}

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

Aenumerated

Benumerate

Cindexed

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name that does not exist like 'enumerate' or 'indexed'.

Forgetting the parentheses after the method name.

The enumerated() method returns a sequence of pairs (index, element) for arrays.

3fill in blank

hard

Fix the error in the loop to correctly access index and value.

Swift

let numbers = [10, 20, 30]
for ([1], value) in numbers.enumerated() {
    print("Index: \([1]), Value: \(value)")
}

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

Ai

Bvalue

Cnum

Dindex

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for the index in the loop and print statement.

Using the value variable name instead of index.

The variable index is used to hold the index from enumerated(). It must be consistent in the loop and print statement.

4fill in blank

hard

Fill both blanks to create a dictionary with words as keys and their lengths as values, filtering words longer than 4 letters.

Swift

let words = ["apple", "dog", "banana", "cat"]
let wordLengths = [[1]: [2] for word in words where word.count > 4]

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

Aword

Bword.count

Cword.length

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using word.length which is not valid in Swift.

Using a variable name not declared.

The dictionary comprehension uses word as the key and word.count as the value. The filter keeps words longer than 4 letters.

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase words as keys, their lengths as values, filtering words with length greater than 3.

Swift

let words = ["sun", "moon", "star", "sky"]
let result = [[1]: [2] for word in words where [3]]

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

Aword.uppercased()

Bword.count

Cword.count > 3

Dword.lowercased()

Attempts:

3 left

💡 Hint

Common Mistakes

Using word.lowercased() instead of uppercase.

Using incorrect filter condition.

The dictionary keys are uppercase words using word.uppercased(). Values are word lengths with word.count. The filter keeps words longer than 3 letters.

Practice

1. What does the enumerated() method do when used on an array in Swift?

easy

A. It provides both the index and the value of each element during iteration.

B. It reverses the order of the array elements.

C. It filters out duplicate elements from the array.

D. It sorts the array in ascending order.

Solution

1. Step 1: Understand the purpose of enumerated()

   The enumerated() method returns a sequence of pairs (index, value) for each element in the array.

2. Step 2: Identify what is returned during iteration

   Each iteration gives you the position (index) and the element itself (value), allowing you to use both.

3. Final Answer:

   It provides both the index and the value of each element during iteration. -> Option A

4. Quick Check:

   enumerated() = index + value [OK]

Hint: Remember: enumerated() gives index and item together [OK]

Common Mistakes:

• Thinking enumerated() changes array order
• Believing enumerated() filters or sorts elements
• Confusing enumerated() with map or filter

2. Which of the following is the correct syntax to iterate over an array fruits using enumerated() in Swift?

easy

A. for (index, fruit) in fruits.enumerated() { print(index, fruit) }

B. for index, fruit in fruits { print(index, fruit) }

C. for index, fruit in fruits.enumerated { print(index, fruit) }

D. for (fruit, index) in fruits.enumerated() { print(index, fruit) }

Solution

1. Step 1: Check the correct use of enumerated()

   The method enumerated() must be called with parentheses to return the sequence.

2. Step 2: Verify tuple unpacking syntax

   The for loop must unpack the tuple as (index, value) in parentheses.

3. Final Answer:

   for (index, fruit) in fruits.enumerated() { print(index, fruit) } -> Option A

4. Quick Check:

   Correct syntax = for (index, fruit) in fruits.enumerated() { print(index, fruit) } [OK]

Hint: Use parentheses with enumerated() and tuple unpacking [OK]

Common Mistakes:

• Omitting parentheses after enumerated()
• Swapping index and value order in tuple
• Trying to unpack without parentheses

3. What will be the output of the following Swift code?

let animals = ["cat", "dog", "bird"]
for (i, animal) in animals.enumerated() {
    print("\(i): \(animal)")
}

medium

A. cat: 0
dog: 1
bird: 2

B. 1: cat
2: dog
3: bird

C. 0: cat
1: dog
2: bird

D. cat
dog
bird

Solution

1. Step 1: Understand enumerated() output

   enumerated() gives index starting at 0 and the element value.

2. Step 2: Trace the print statements

   Each line prints index, colon, space, then the animal name.

3. Final Answer:

   0: cat 1: dog 2: bird -> Option C

4. Quick Check:

   Index starts at 0, prints index: value [OK]

Hint: Indexes start at 0 unless adjusted [OK]

Common Mistakes:

• Assuming index starts at 1
• Printing value before index
• Ignoring the colon and space formatting

4. Identify the error in the following Swift code snippet:

let numbers = [10, 20, 30]
for index, value in numbers.enumerated {
    print(index, value)
}

medium

A. print statement syntax is invalid.

B. Incorrect variable names in the for loop.

C. Array declaration syntax is wrong.

D. Missing parentheses after enumerated() method call.

Solution

1. Step 1: Check method call syntax

   The method enumerated must be called with parentheses: enumerated().

2. Step 2: Verify other parts of the code

   Variable names and array declaration are correct; print syntax is valid.

3. Final Answer:

   Missing parentheses after enumerated() method call. -> Option D

4. Quick Check:

   enumerated() needs () [OK]

Hint: Always add () after enumerated [OK]

Common Mistakes:

• Forgetting parentheses after enumerated
• Swapping index and value order
• Using wrong print syntax

5. Given an array scores = [85, 92, 78, 90], write Swift code using enumerated() to print each score with its position starting from 1, like "Player 1: 85". Which code snippet correctly does this?

hard

A. for score in scores { print("Player \(score): \(score)") }

B. for (index, score) in scores.enumerated() { print("Player \(index + 1): \(score)") }

C. for (index, score) in scores.enumerated() { print("Player \(index): \(score)") }

D. for (score, index) in scores.enumerated() { print("Player \(index + 1): \(score)") }

Solution

1. Step 1: Use enumerated() to get index and score

   enumerated() returns (index, value) tuples; index starts at 0.

2. Step 2: Adjust index to start from 1 in print

   Add 1 to index when printing to start counting players from 1.

3. Final Answer:

   for (index, score) in scores.enumerated() { print("Player \(index + 1): \(score)") } -> Option B

4. Quick Check:

   Index + 1 for counting players [OK]

Hint: Add 1 to index to start counting from 1 [OK]

Common Mistakes:

• Printing index without adding 1
• Swapping index and value in tuple
• Using wrong tuple unpacking order