Swift REPL and Playgrounds - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Swift REPL variable mutation

What is the output of the following Swift REPL code snippet?

Swift

var greeting = "Hello"
greeting += ", world!"
print(greeting)

A Hello, world

B Hello world

C Hello world!

D Hello, world!

💡 Hint

Look carefully at the string concatenation and punctuation.

The variable greeting starts as "Hello" and then ", world!" is appended, resulting in "Hello, world!".

🧠 Conceptual

intermediate

Purpose of Swift Playgrounds

Which of the following best describes the main purpose of Swift Playgrounds?

A To compile large Swift projects for production

B To write and test Swift code interactively with immediate feedback

C To manage Swift package dependencies

D To deploy Swift apps to the App Store

💡 Hint

Think about what makes Playgrounds different from full IDEs.

Swift Playgrounds is designed for learning and experimenting with Swift code interactively, giving immediate results.

❓ Predict Output

advanced

Output of Swift REPL code with optional binding

What is the output of this Swift REPL code?

Swift

let numberString: String? = "42"
if let number = numberString, number == "42" {
    print("Number is 42")
} else {
    print("Number is not 42")
}

A Compilation error

B Number is not 42

C Number is 42

D Runtime error

💡 Hint

Check the optional binding and string comparison carefully.

The optional string contains "42", so the if condition is true and prints "Number is 42".

🔧 Debug

advanced

Identify the error in Swift Playground code

What error will this Swift Playground code produce?

Swift

var count = 5
count = "five"
print(count)

A Type error: Cannot assign value of type 'String' to type 'Int'

B Runtime error: Unexpected nil value

C Syntax error: Missing semicolon

D No error, prints 'five'

💡 Hint

Check the variable type and assignment compatibility.

Variable count is declared as Int, but assigned a String, causing a type error.

🚀 Application

expert

Result of running Swift Playground code with closures

What is the output of this Swift Playground code snippet?

Swift

let numbers = [1, 2, 3, 4, 5]
let doubled = numbers.map { num in
    num * 2
}
print(doubled)

A [2, 4, 6, 8, 10]

B [1, 2, 3, 4, 5]

C Compilation error due to missing return

D Runtime error: nil value

💡 Hint

Remember how the map function transforms each element.

The map function doubles each number, resulting in [2, 4, 6, 8, 10].