Why Swift loops are safe by default - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a safe Swift for-in loop

What is the output of this Swift code snippet?

Swift

let numbers = [1, 2, 3, 4, 5]
var sum = 0
for number in numbers {
    sum += number
}
print(sum)

A Compilation error

B 10

C 0

D 15

💡 Hint

Think about what the loop does to the sum variable.

The loop safely iterates over each element in the array and adds it to sum. The total sum of 1+2+3+4+5 is 15.

🧠 Conceptual

intermediate

Why Swift loops prevent out-of-bounds errors

Why do Swift loops like for-in prevent out-of-bounds errors when iterating over arrays?

A Because Swift checks the array bounds automatically during iteration

B Because Swift disables array bounds checking for performance

C Because Swift allows accessing any index without checks

D Because Swift requires manual index checks inside loops

💡 Hint

Think about how Swift protects you from common mistakes.

Swift's for-in loop automatically iterates over valid elements only, preventing out-of-bounds access by design.

🔧 Debug

advanced

Identify the runtime error in this Swift loop

What error will this Swift code produce when run?

Swift

let array = [10, 20, 30]
for i in 0...array.count {
    print(array[i])
}

A Index out of range runtime error

B Compilation error due to invalid syntax

C No error, prints all elements

D Prints all elements plus nil

💡 Hint

Check the range used in the loop and array indices.

The loop uses 0...array.count which includes an index equal to array.count, causing an out-of-bounds runtime error.

📝 Syntax

advanced

Which Swift loop syntax is safe and correct?

Which option shows a safe and correct way to loop through an array in Swift?

A for i in 1..<array.count { print(array[i]) }

B for i in 0..<array.count { print(array[i]) }

C for i in 1...array.count { print(array[i]) }

D for i in 0...array.count { print(array[i]) }

💡 Hint

Remember Swift arrays start at index 0 and last index is count - 1.

Option B uses a half-open range 0..

🚀 Application

expert

Predict the output of a nested safe Swift loop

What is the output of this Swift code?

Swift

let matrix = [[1, 2], [3, 4], [5, 6]]
var total = 0
for row in matrix {
    for value in row {
        total += value
    }
}
print(total)

A Compilation error

B 20

C 21

D Runtime error

💡 Hint

Add all numbers in the nested arrays carefully.

The nested loops safely iterate all elements in the 2D array and sum them: 1+2+3+4+5+6 = 21.