Array iteration and enumerated in Swift - Mini Project: Build & Apply

Array iteration and enumerated

📖 Scenario: You are helping a small bookstore keep track of book titles and their positions on a shelf.

🎯 Goal: You will create an array of book titles, then use enumerated() to print each book's position and title.

📋 What You'll Learn

Create an array called books with exactly these titles: "Swift Basics", "iOS Development", "Data Structures"

Create a variable called startIndex and set it to 1

Use a for loop with enumerated() on books to get index and title

Print the position starting from startIndex and the book title in the format: "Book 1: Swift Basics"

💡 Why This Matters

🌍 Real World

Bookstores or libraries often need to list items with their positions or numbers for easy reference.

💼 Career

Knowing how to loop through arrays with indexes is important for many programming tasks like displaying lists, processing data, or creating menus.

1

Create the books array

Create an array called books with these exact titles in order: "Swift Basics", "iOS Development", "Data Structures"

Swift

# Create the array books with the given titles
# Your code here

Hint

Use square brackets [] to create an array and separate titles with commas.

2

Set the start index

Create a variable called startIndex and set it to 1

Swift

let books = ["Swift Basics", "iOS Development", "Data Structures"]
# Create startIndex variable and set it to 1
# Your code here

Hint

Use let to create a constant variable named startIndex.

3

Loop with enumerated()

Use a for loop with enumerated() on books to get index and title

Swift

let books = ["Swift Basics", "iOS Development", "Data Structures"]
let startIndex = 1
# Use for loop with enumerated() to get index and title
# Your code here

Hint

Use for (index, title) in books.enumerated() to get both position and value.

4

Print book positions and titles

Inside the loop, print the position starting from startIndex plus index and the book title in this exact format: "Book 1: Swift Basics"

Swift

let books = ["Swift Basics", "iOS Development", "Data Structures"]
let startIndex = 1
for (index, title) in books.enumerated() {
    # Print the book position and title here
    # Your code here
}

Hint

Use print("Book \(startIndex + index): \(title)") inside the loop.

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