Conditions

How to check a condition is true or false

Basic syntax

if someCondition {
    print("Do something")
}

Braces signal the start and end of a code block.

let score = 65

if score > 80 {
    // won't run
    print("Great job!")
}

Another example

let speed = 88
let percentage = 85
let age = 18

if speed >= 88 {
    print("Where we're going, we don't need roads.")
}

if percentage < 85 {
    print("Sorry you failed the test.")
}

if age >= 18 {
    print("You're eligible to vote")
}

Another example

let ourName = "Dave Lister"
let friendName = "Arnold Rimmer"

if ourName < friendName {
    print("It's \(ourName) vs \(friendName)")
}

if ourName > friendName {
    print("It's \(friendName) vs \(ourName)")
}

Another example

var numbers = [1,2,3]

numbers.append(4)

if numbers.count > 3 {
    numbers.remove(at: 0)
}

print(numbers)

String comparison

== means is equal to
!= means is not equal to

Example

let country = "Canada"

if country == "Australia" {
    print("G'day mate")
}

let name = "Taylor Swift"

if name != "Anonymous" {
    print("Welcome \(name)")
}

var username = "@taylorswift123"

if username == "" {
    username = "Anonymous"
}

print("Welcome, \(username)")

Other ways to check truthiness

var username = "@taylorswift123"

if username.isEmtpy == true {
    username = "Anonymous"
}

//

if username.isEmtpy {
    username = "Anonymous"
}

print("Welcome, \(username)")

Note:

With enum types order is important. so:

enum sizes: Comparable {
    case small
    case medium
    case large
}

let a = sizes.small
let b = .large

// This works because small comes before large in the enum list
if a < b {
    print("a is smaller than b")
}

How to check multiple conditions

We want to be able to control the program flow whether something is true or false.
We can do so w the else keyword. Ex:

let age = 16

if age >= 18 {
    print("vote")
} else {
    print("too young")
}

We can use else if for multiple branches of code. Ex:

if a {
    print("a")
} else if b {
    print("b")
} else {
    print("default answer")
}

We can check multiple conditions with the && operator. Ex:

if a && b {
    print("a and b are true")
}

We can check whether one or another condition are true with the || operator. Ex:

if a || b {
    print("a or b is true")
}

Complex conditions! Ex:

enum TransportOption {
    case airplane, helicopter, bicycle, car, escooter
}

// set transport to a case in the TransportOption enum
let transport = TransportOption.airplane

// use shorthand
if transport == .airplane || transport == .helicopter {
    print ("flying")
} else if transport == .bicycle {
    print("riding")
} else if transport == .car {
    print("driving")
} else {
    print("riding a scooter")
}

Thought:

Parentheses are optional but should be used to clarify complex conditionals. Complex meaning multiple conjunctions using && or ||

Scored 9/12 on Conditions. Botched first 2 questions and missed the 5th.
Scored 12/12 on combining conditions.

How to use the switch statements to check multiple conditions

We use switch statements to simplify if/else logic. Ex:

// Given:
enum Weather {
    case .sun
    case .wind
    case .rain
    case .snow
}

switch forecast {
case .sun:
    print("its sunny")
case .wind:
    print("its windy")
case .rain:
    print("its rainy")
case .snow:
    print("its snowing")
case .unknown
    print("what's happening outside?")
}

Caveats to using a switch:

• must have a case for each option, must be exhaustive
• Swift will exit the switch block early if a case is matched
• must provide a default case. Default case must be last because default run’s first and makes the switch statement pointless.
• The default case is not needed in the case of checking enums

Using fallthrough we can continue checking cases even if we have matched a case early. Ex:

let day = 5

switch day {
case 5:
    print("5 golden rings")
    fallthrough
case 4:
    print("4 calling birds")
    fallthrough
case 3:
    print("3 french hens")
    fallthrough
case 2:
    print("2 turtle oves")
    fallthrough
default:
    print("And a partridge in a pear tree")
}

Scored 5/6 on switch statements. Missed q5 re: not needing a default cases when using a switch on an enum data type.

How to use the ternary operator for quick tests

Binary operators operate on 2 pieces of data. Ex:

2 + 5

Ternary operator works on 3 pieces of data. Ex:

let age = 18
let canVote = age >= 18 ? "Yes" : "No"

It is identical to an if/else statement

Ternaries include

• what we are checking
• what to do if the condition is true
• what to do if the condition is false

Ex:

let hour = 23
print(hour < 12 ? "before noon" : "after noon")

let names = ["a", "b", "c"]
let crewCount = names.isEmpty ? "No one" : "\(names.count) people"

enum Theme {
    case light, dark
}
let theme = Theme.dark
let background = theme == .dark ? "black" : "white"
print(background)

Why ternaries?

• they allow us to have an expression evaluate within methods
• conciseness

Scored 12/12 on Ternary