Struct declaration syntax in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple struct instance

What is the output of this Swift code when run?

Swift

struct Person {
    var name: String
    var age: Int
}

let p = Person(name: "Anna", age: 30)
print(p.name)

A Anna

B 30

C Person(name: "Anna", age: 30)

D Error: Missing initializer

💡 Hint

Look at what property is printed from the struct instance.

The code creates a Person struct with name and age. Printing p.name outputs the string "Anna".

❓ Predict Output

intermediate

Value of a struct property after modification

What is the value of the property 'age' after running this Swift code?

Swift

struct Animal {
    var species: String
    var age: Int
}

var dog = Animal(species: "Dog", age: 5)
dog.age = 6
print(dog.age)

A 6

B 5

C Error: Cannot assign to property

D 0

💡 Hint

Check if the struct instance is declared as variable or constant.

Since 'dog' is declared with 'var', its properties can be changed. The age is updated to 6.

❓ Predict Output

advanced

Output of struct with method

What does this Swift code print?

Swift

struct Rectangle {
    var width: Int
    var height: Int
    func area() -> Int {
        return width * height
    }
}

let rect = Rectangle(width: 3, height: 4)
print(rect.area())

A 7

B Error: Missing return statement

C 12

D 0

💡 Hint

Multiply width and height to get the area.

The area method returns width * height, which is 3 * 4 = 12.

❓ Predict Output

advanced

Error raised by incorrect struct declaration

What error does this Swift code produce?

Swift

struct Car {
    var model: String
    var year: Int

    func description() -> String {
        return "Model: \(model), Year: \(year)"
    }
}

let myCar = Car(model: "Tesla")

A No error, compiles and runs fine

B Error: Missing argument for parameter 'year' in call

C Error: Cannot assign to property 'model' in initializer

D Error: Method description missing return type

💡 Hint

Check if all stored properties have values after init.

The struct has two stored properties but the init only sets 'model'. 'year' is not initialized, causing a compile error.

🧠 Conceptual

expert

Number of items in a struct array after filtering

Given this Swift code, how many items remain in the 'youngPeople' array after filtering?

Swift

struct Person {
    var name: String
    var age: Int
}

let people = [
    Person(name: "John", age: 20),
    Person(name: "Jane", age: 17),
    Person(name: "Bob", age: 25),
    Person(name: "Alice", age: 16)
]

let youngPeople = people.filter { $0.age < 18 }
print(youngPeople.count)

A 3

B 4

C 1

D 2

💡 Hint

Count how many people have age less than 18.

Jane (17) and Alice (16) are under 18, so 2 items remain after filtering.