Optional declaration with ? suffix in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift code with optional?

Consider the following Swift code. What will be printed when it runs?

Swift

var name: String? = "Alice"
print(name)

A Optional("Alice")

B Alice

C nil

D Error: Variable 'name' not initialized

💡 Hint

Remember that printing an optional variable shows it wrapped in Optional(...) if it has a value.

In Swift, an optional variable holds either a value or nil. Printing an optional directly shows Optional(value) if it has a value.

❓ Predict Output

intermediate

What is the value of 'age' after this code runs?

Look at this Swift code snippet. What is the value of 'age' after execution?

Swift

var age: Int? = nil
age = 30

A Optional(30)

B nil

C 30

D Error: Cannot assign non-optional to optional

💡 Hint

Assigning a non-optional value to an optional variable wraps it automatically.

Assigning 30 to 'age' wraps it as Optional(30). The variable 'age' is still optional but holds the value 30.

❓ Predict Output

advanced

What error does this code produce?

What error will this Swift code cause when compiled?

Swift

var score: Int? = 10
var total: Int = score + 5

A Syntax error: Missing optional unwrapping

B No error, total is 15

C Runtime error: nil value unwrapped

D Type error: Cannot add 'Int?' and 'Int'

💡 Hint

You cannot directly add an optional Int and a non-optional Int without unwrapping.

The compiler does not allow adding an optional Int and an Int directly. You must unwrap the optional first.

🧠 Conceptual

advanced

Which statement about optional declaration with '?' is true?

Choose the correct statement about declaring variables with '?' in Swift.

A Variables with '?' cannot be assigned nil after initialization.

B A variable declared with '?' must always have a value assigned.

C A variable declared with '?' can hold a value or nil.

D Using '?' means the variable is a constant and cannot change.

💡 Hint

Think about what '?' means in Swift variable declarations.

The '?' suffix means the variable is optional and can hold a value or nil.

❓ Predict Output

expert

What is the output of this Swift optional chaining code?

Analyze the code and select the output printed.

Swift

class Person {
    var pet: Pet?
}

class Pet {
    var name: String
    init(name: String) { self.name = name }
}

let person = Person()
print(person.pet?.name ?? "No pet")

A Optional(nil)

B No pet

C nil

D Runtime error: Unexpected nil

💡 Hint

Optional chaining returns nil if any part is nil, and the nil-coalescing operator provides a default.

Since 'person.pet' is nil, 'person.pet?.name' is nil, so the default "No pet" is printed.