Nil represents absence of value in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to assign nil to the optional variable.

Swift

var name: String? = [1]

Drag options to blanks, or click blank then click option'

Afalse

B""

C0

Dnil

Attempts:

3 left

💡 Hint

Common Mistakes

Using empty string "" instead of nil for optional variables.

Assigning 0 or false to a String optional.

In Swift, nil means the variable has no value. Optional variables can hold nil.

2fill in blank

medium

Complete the code to safely unwrap the optional using if let.

Swift

if let unwrappedName = name [1] {
    print("Name is \(unwrappedName)")
}

Drag options to blanks, or click blank then click option'

A== nil

B!=

C=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using == nil which checks for nil instead of unwrapping.

Using = which is assignment, not comparison.

The if let syntax unwraps the optional only if it is not nil. The condition uses != implicitly.

3fill in blank

hard

Fix the error in force unwrapping the optional variable.

Swift

let forcedName = name[1]

Drag options to blanks, or click blank then click option'

A!

B?

C.

D:

Attempts:

3 left

💡 Hint

Common Mistakes

Using ? instead of ! for force unwrapping.

Using dot or colon which are invalid here.

Force unwrapping an optional uses ! to get the value directly, but it crashes if nil.

4fill in blank

hard

Fill both blanks to create a dictionary with optional values and check for nil.

Swift

let ages: [String: Int?] = ["Alice": [1], "Bob": [2]]
if ages["Alice"] [2] nil {
    print("Alice's age is known")
}

Drag options to blanks, or click blank then click option'

Anil

B25

C!=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning nil to Alice when we want a known age.

Using == instead of != in the if condition.

The dictionary holds optional Int values. Assign 25 to Alice and check if the value is not nil.

5fill in blank

hard

Fill all three blanks to unwrap an optional with guard and provide a default value.

Swift

func greet(_ name: String?) {
    guard let unwrappedName = name [1] else {
        print("Hello, [2]!")
        return
    }
    print("Hello, [3]!")
}

Drag options to blanks, or click blank then click option'

A!=

BGuest

CunwrappedName

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of != in the guard condition.

Printing the optional variable instead of the unwrapped one.

The guard statement unwraps the optional if it is not nil. Otherwise, it greets a default name 'Guest'.