Conditionals

`if` Statement

An if statement executes a code block when its condition evaluates to true. If the condition is false, the code block does not execute.

var halloween = true 

if halloween {
  print("Trick or treat!")
}

// Prints: Trick or treat!

`else` Statement

An else statement is a partner to an if statement. When the condition for the if statement evaluates to false, the code within the body of the else will execute.

var turbulence = false 

if turbulence {
  print("Please stay seated.")
} else {
  print("You may freely move around.")
}

// Prints: You may freely move around.

`else if` Statement

An else if statement provides additional conditions to check for within a standard if/else statement. else if statements can be chained and exist only after an if statement and before an else.

var weather = "rainy" 

if weather == "sunny" {
  print("Grab some sunscreen")
} else if weather == "rainy" {
  print("Grab an umbrella")
} else if weather == "snowing" {
  print("Wear your snow boots")
} else {
  print("Invalid weather")
}

// Prints: Grab an umbrella

Comparison Operators

Comparison operators compare the values of two operands and return a Boolean result:

< less than
> greater than
<= less than or equal to
>= greater than or equal to
== equal to
!= not equal to

5 > 1       // true 
6 < 10      // true 
2 >= 3      // false
3 <= 5      // true
"A" == "a"  // false
"B" != "b"  // true

Ternary Conditional Operator

The ternary conditional operator, denoted by a ?, creates a shorter alternative to a standard if/else statement. It evaluates a single condition and if true, executes the code before the :. If the condition is false, the code following the : is executed.

var driverLicense = true

driverLicense ? print("Driver's Seat") : print("Passenger's Seat") 

// Prints: Driver's Seat

`switch` Statement

The switch statement is a type of conditional used to check the value of an expression against multiple cases. A case executes when it matches the value of the expression. When there are no matches between the case statements and the expression, the default statement executes.

var secondaryColor = "green"

switch secondaryColor {
  case "orange":
    print("Mix of red and yellow")
  case "green":
    print("Mix of blue and yellow")
  case "purple":
    print("Mix of red and blue") 
  default: 
    print("This might not be a secondary color.") 
}

// Prints: Mix of blue and yellow

`switch` Statement: Interval Matching

Intervals within a switch statement’s case provide a range of values that are checked against an expression.

let year = 1905
var artPeriod: String

switch year {
  case 1860...1885:
    artPeriod = "Impressionism"
  case 1886...1910:
    artPeriod = "Post Impressionism"
  case 1912...1935: 
    artPeriod = "Expressionism"
  default:  
    artPeriod = "Unknown"
}

// Prints: Post Impressionism

`switch` Statement: Compound Cases

A compound case within a switch statement is a single case that contains multiple values. These values are all checked against the switch statement’s expression and are separated by commas.

let service = "Seamless"

switch service {
  case "Uber", "Lyft":
    print("Travel")
  case "DoorDash", "Seamless", "GrubHub":
    print("Restaurant delivery")
  case "Instacart", "FreshDirect":
    print("Grocery delivery")
  default: 
    print("Unknown service")
}

// Prints: Restaurant delivery

`switch` Statement: `where` Clause

Within a switch statement, a where clause is used to test additional conditions against an expression.

let num = 7

switch num {
  case let x where x % 2 == 0:
    print("\(num) is even")
  case let x where x % 2 == 1:
    print("\(num) is odd")
  default:
    print("\(num) is invalid")
}

// Prints: 7 is odd