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Optionals.md

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Optionals Exercises

Question 1

a. Given the variable userNameOne below, print "The username is Test User". Use Optional Binding (if let) to print the name.

var userNameOne: String? = "Test User"
Solution 
var userNameOne: String? = "Test User"
if let name = userNameOne {
  print("The username is \(name)") // The username is Test User
}

b. Given the variable userNameTwo below, print "The username is undefined". Use the nil coalescing operator (??).

var userNameTwo: String? = nil
Solution 
var userNameTwo: String? = nil
print(userNameTwo ?? "The username is undefined.") // The username is undefined.

Question 2

a. Given the variables rectOneWidth and rectOneHeight below, print "The area of rectOne is 50". Use Optional Binding (if let) to print the area.

var rectOneWidth: Double? = 5
var rectOneHeight: Double? = 10
Solution 
var rectOneWidth: Double? = 5
var rectOneHeight: Double? = 10

if let rectOneWidth = rectOneWidth,
   let rectOneHeight = rectOneHeight {
  print("The are of rectOne is \(rectOneWidth * rectOneHeight)") // The are of rectOne is 50.0
}

b. Given the variables rectTwoWidth and rectTwoHeight below, print "The are of rectTwo is not able to be calculated". Use Optional Binding (if let) to print this message.

var rectTwoWidth: Double? = nil
var rectTwoHeight: Double? = nil
Solution 
var rectTwoWidth: Double? = nil
var rectTwoHeight: Double? = nil

if let rectTwoWidth = rectTwoWidth,
   let rectTwoHeight = rectTwoHeight {
  print("The area of rectTwo is \(rectTwoWidth * rectTwoHeight)")
} else {
  print("The area of rectTwo is not able to be calculated.")
}

Question 3

a. Given the variables userOneName, userOneAge, and userOneHeight below, write code that prints "Hello Anne! You are 15 years old and 5.8 feet tall" (1 foot = 12 inches). Use optional binding.

var userOneName: String? = "Anne"
var userOneAge: Int? = 15
var userOneHeight: Double? = 70
Solution 
var userOneName: String? = "Anne"
var userOneAge: Int? = 15
var userOneHeight: Double? = 70

if let userOneName = userOneName,
   let userOneAge = userOneAge,
   let userOneHeight = userOneHeight {
  let height = String(format: "%.1f", Double(userOneHeight) / Double(12.0))
  print("Hello \(userOneName)! You are \(userOneAge) years old and \(height) feet tall.")
  // Hello Anne! You are 15 years old and 5.8 feet tall.
}

b. Given the variables userTwoName, userTwoAge and userTwoHeight below, write code that prints "Hello user! You are 15 years old and I don't know how tall you are". Use optional binding

var userTwoName: String? = nil
var userTwoAge: Int? = 15
var userTwoHeight: Double? = nil
Solution 
var userTwoName: String? = nil
var userTwoAge: Int? = 15
var userTwoHeight: Double? = nil

if let userTwoName = userTwoName,
   let userTwoAge = userTwoAge,
   let userTwoHeight = userTwoHeight {
  let height = String(format: "%.1f", Double(userTwoHeight) / Double(12.0))
  print("Hello \(userTwoName)! You are \(userTwoAge) years old and \(height) feet tall.")
} else {
  print("Hello user! You are 15 years old and I don't know how tall you are.")
  // Hello user! You are 15 years old and I don't know how tall you are.
}

Question 4

Give the variable favoriteNumber, write code that either prints "Your favorite number is " followed by the number, or "I don't know what your favorite number is"

favoriteNumber is of type Int? and will either be nil or a random number between 0 and 10. It will change each time you run your Playground.

var favoriteNumber = Bool.random() ? Int.random(in: 0...10) : nil
Solution 
var favoriteNumber = Bool.random() ? Int.random(in: 0...10) : nil

if let favoriteNumber = favoriteNumber {
  print("Your favorite number is \(favoriteNumber)")
} else {
  print("I don't know what your favorite number is.")
}

Question 5

Given the variables numOne, numTwo and numThree, write code that prints "The sum of all the numbers is " followed by their sum. If a number is nil, don't add it to the sum. If all numbers are nil, the sum is zero.

var numOne = Bool.random() ? Int.random(in: 0...10) : nil
var numTwo = Bool.random() ? Int.random(in: 0...10) : nil
var numThree = Bool.random() ? Int.random(in: 0...10) : nil
Solution 
var numOne = Bool.random() ? Int.random(in: 0...10) : nil
var numTwo = Bool.random() ? Int.random(in: 0...10) : nil
var numThree = Bool.random() ? Int.random(in: 0...10) : nil

var sum = 0
if numOne == nil && numTwo == nil && numThree == nil {
  print("The sum is zero.")
} else {
  if let numOne = numOne,
     let numTwo = numTwo,
     let numThree = numThree {
    print("The sum of all the numbers is \(numOne + numTwo + numThree).")
  }
  if let numOne = numOne {
    sum += numOne
  }
  if let numTwo = numTwo {
    sum += numTwo
  }
  if let numThree = numThree {
    sum += numThree
  }
  print("The sum is \(sum).")
}

Question 6

a. Given the variable numbers below, write code that prints "The sum of all the numbers is " followed by their sum. If a number is nil, don't add it to the sum. If all numbers are nil, the sum is zero.

var numbers = [Int?]()

for _ in 0..<10 {
    numbers.append(Bool.random() ? Int.random(in: 0...100) : nil)
}
Solution 
var numbers = [Int?]()

for _ in 0..<10 {
    numbers.append(Bool.random() ? Int.random(in: 0...100) : nil)
}

var totalSum = 0
for num in numbers {
  totalSum += (num ?? 0)
}

b. Using the same variable, find the average of all non-nil values.

Solution 
let nonNilValues = numbers.compactMap { $0 }

let nonNilValuesSum = nonNilValues.reduce(0, +)
print("The average of all the non nil values is \(nonNilValuesSum / nonNilValues.count)")