Array iteration and enumerated in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of enumerated array iteration

What is the output of this Swift code?

Swift

let fruits = ["Apple", "Banana", "Cherry"]
for (index, fruit) in fruits.enumerated() {
    print("\(index): \(fruit)")
}

A

Apple: 0
Banana: 1
Cherry: 2

B

1: Apple
2: Banana
3: Cherry

C

0: Apple
1: Banana
2: Cherry

D

Apple
Banana
Cherry

💡 Hint

Remember that enumerated() gives pairs of (index, element) starting at 0.

The enumerated() method returns a sequence of pairs (index, element) starting from 0. The loop prints the index and fruit separated by a colon.

❓ Predict Output

intermediate

Enumerated index starting value

What will be printed by this Swift code?

Swift

let numbers = [10, 20, 30]
for (index, number) in numbers.enumerated() {
    print(index + 1, number)
}

A

1 20
2 30
3 40

B

0 10
1 20
2 30

C

10 1
20 2
30 3

D

1 10
2 20
3 30

💡 Hint

The index from enumerated() starts at 0, but the code adds 1 before printing.

The enumerated() method starts index at 0, but the code prints index + 1, so indexes start at 1 in output.

🔧 Debug

advanced

Why does this enumerated loop cause an error?

This Swift code causes a compile error. What is the reason?

Swift

let items = ["a", "b", "c"]
for index, item in items.enumerated() {
    print(index, item)
}

A The array 'items' is empty

B Missing parentheses around (index, item) in the for loop

C The variable 'item' is not declared

D Cannot use enumerated() on arrays

💡 Hint

Check the syntax for tuple unpacking in for loops.

In Swift, when unpacking tuples in a for loop, parentheses are required around the variables: for (index, item) in ...

❓ Predict Output

advanced

Output of modifying array during enumerated iteration

What is the output of this Swift code?

Swift

var letters = ["x", "y", "z"]
for (i, letter) in letters.enumerated() {
    letters[i] = letter.uppercased()
}
print(letters)

A ["X", "Y", "Z"]

B ["x", "y", "z"]

C ["X", "y", "z"]

D Runtime error: Concurrent modification

💡 Hint

Think about whether modifying elements by index during iteration is allowed.

The code modifies each element by index during iteration, which is allowed. The letters become uppercase.

🧠 Conceptual

expert

Count of elements after filtering with enumerated

Given this Swift code, how many elements will be in the filtered array?

Swift

let values = [5, 10, 15, 20, 25]
let filtered = values.enumerated().filter { index, value in
    index % 2 == 0 && value > 10
}.map { $0.element }
print(filtered.count)

A 2

B 1

C 3

D 4

💡 Hint

Check which elements have even index and value greater than 10.

Indexes 0, 2, 4 are even. Values at these indexes are 5, 15, 25. Only 15 and 25 are > 10, so 2 elements. But 5 is not > 10, so filtered elements are 15 and 25. Wait, 15 at index 2 and 25 at index 4. So count is 2.