Different types of variables

var petsAge = 12
var myMiddleInitial: Character = "A"
var numberOfWheels: Int = 4
var centimetersOfRainfall: Float = 5.5
var pi: Double = 3.14159265359
var letterOfTheDay: Character = "z"
var myFavoriteAnimal: String = "nudibranch"
var rainingOutside: Bool = true

let encouragement = "you can do it!"
var customizedEncouragement = "you can do it, stephanie!"
customizedEncouragement = "you can do it, Ryder!"

let birthYear = 2008
var currentYear = 2017
var age = currentYear - birthYear
currentYear = 2017
age = currentYear - birthYear

Names cannot contain whitespace characters, mathematical symbols, arrows and [a few other obscure characters].
Names must begin with an uppercase or lowercase letter A through Z, an underscore, or [a few other less common options].

let theTrue = "Money can't buy me love."

var characterPoorString = ""
let stringWithPotential = String()