Declare an Integer

let myInt : Int
// or
let anotherInt = 4

Declare a String

let firstName : String
firstName = "John"
// or
let lastName = "Doe"

Declare a Double with type inference

let myDouble = 4.5

Declare an empty String

let emptyString = ""
// or
let anotherEmptyString = String()

Iterate through the characters of a String

for character in myString.characters {
  print(character)
}

Count the numbers of characters of a String

let myString = "Hello"
print(myString.characters.count)

Get the first character of a String

var myString = "Hello"
myString[myString.startIndex] // is H
// but returns an error for an empty String

Get the n-th character of a String

let myString = "Hello"
myString.startIndex.advancedBy(4) // is "o"

Replace a substring of a String by another String

let myString = "Hello"
let stringToFind = "l"
let stringToReplace = "LL"
myString.stringByReplacingOccurrencesOfString(stringToFind
, withString : stringToReplace) // is "HeLLLLo"

Test the beginning of a String and the end of a String

"Hello".hasPrefix("He") // returns true
"Hello".hasPrefix("el") // returns false
"Hello".hasSuffix("lo") // returns true

Declare an empty Array of Integers.

Add one item.

var myInts = [Int]()
myInts.append(18)

Create an Array of String with elements

var shoppingList = ["eggs", "milk", "bread"]

Count the number of elements of an Array

myArray.count

Test if an Array is empty

myArray.isEmpty

Get the element of an Array at a given index

let myArray = [ 2, 4, 5]
myArray[0] // returns 2
myArray[2] // return 5
myArray[3] // returns an Error at runtime

Change the value of an Array at a given index

let myArray = [ 4, 5 , 6]
myArray[1] = 7
// myArray is now : [4 , 7 , 6]

Test if an Array includes a given value.

let myArray = ["John", "Paul", "Gringo"]
myArray.contains("Paul") // returns 1
myArray.contains("Toto") // returns nil

Get subarray from an Array with a range

ley myArray = ["apples", "bananas", "pears", "tomatoes"]
myArray[1...2] // is ["bananas", "pears"]

Create an empty Dictionary where the Key is a String, the value an Int.

Add one element.

var ages = [String : Int]()
ages["John"] = 18

Test if a Dictionary is empty.

Count the elements of a Dictionary.

myDictionary.isEmpty
myDictionary.count

Get the value at a given Key in a Dictionary

ley myDict = ["John" : 14, "Paul" : 12]
myDict["John"] // returns 14
myDict["Bill"] // returns nil

Iterate over the keys and values of a Dictionary

for (key, value) in myDictionary {
  // do something with key and value
}

Iterate over the keys of a Dictionary

for key in myDictionary.keys {
  // do something with key
} 

Iterate over the values of a Dictionary

for value in myDictionary.values {
  // do something with value
} 

Create a Dictionary where keys and values are Int

let myDict = [ 1 : 18, 2 : 56]