Can someone please help answer some swift programming questions?

Question 21

Which of the following declares a variable that is an implicitly unwrapped optional Double?

var income: Double

var income: Double = 124300.0

var income: Double?

var income: Double!

Question 22

An implicitly unwrapped optional gives permission for the optional to be unwrapped automatically whenever it is used.

True

False

Question 23

Given the following Swift code:

var age: Int? = 20 if let age = age { print(age) }

For the line "if let age = age {", which of the following is true?

If age on the right of the = is not nil, then the age on the left of the = is the unwrapped value of age.

If age on the right of the = is nil, then the code in the if statement executes.

The age on the left of the = is tested to see if it is the same as the age on the right of the =.

Question 24

Given the following code: var temperature: Double? = 98.6 if (temperature != nil) { print(temperature!) } else { print("The temperature has no value.") } What is the purpose of the exclamation mark after temperature in print(temperature!)?

To declare temperature as an implicitly unwrapped optional.

To make temperature an optional.

To force unwrap the temperature's optional value.

To invoke an exception.

To make the universe collapse into a wormhole.

It generates an error message in the error log with the value of temperature in it.

It bolds the temperature when it is printed.

Question 25

The following code takes the string "49.95", constructs an Double from it, and assigns it to a variable called cost.

var cost = Double("49.95")

Not every string that can be passed to Double() to create a Double is a valid Double value. For example "Mizzou" does not represent a Double, so Double("Mizzou") can't create a Double.

Given this, what type is cost implicitly set to in the following line of code? var cost = Double("49.95")

nil

Double

Double?

Double!

Question 26

String, Array, and Dictionary are implemented as structures in Swift.

True

False

Question 27

Given: struct Font { var name: String var size: Double } Which of the following is the correct line of Swift code for creating an instance of a Font with a name of "times" and a size of 12.0?

let font = new Font(name: "times", size: 12.0)

let font = Font(name: "times", size: 12.0)

let font = Font("times", 12.0)

let font = new Font("times", 12.0)

Question 28

The === operator in Swift is used to do which of the following?

To test if two variables hold the same value.

To test if two variables refer to the same instance of a class.

To test if two instances have the same methods.

To test if a type and optional type refer to the same value.

Question 29

Given: struct Circle { var x = 0.0, y = 0.0, width = 0.0 } var circle = Circle()

Which of the following is used to set the width property of circle to 10.0 in Swift?

circle["width"] = 10.0

circle.setWidth(10.0)

circle.width = 10.0

circle->width = 10.0

Question 30

Given: struct Circle { var x = 0.0, y = 0.0, width = 0.0 } let circle = Circle()

Is the following allowed?

circle.x = 12.3

Yes

No