Day2 (operation)/(optional Value of double eye Value)

let secondSystem:Int = 0b10001

let eightSystem:Int  = 0o21

let tenSystem:Int    = 17

let sixthSystem:Int  = 0x11

// summary: 1.u need insert a "Enter" behind equal symbol

let num_a:Float = 1

let num_b:Int = 1

let a:Int = 3

let b:Double = 0.1415926

let pi:Double = Double(a) + b

// summary: 2.it need change two number‘s type in the same ,in order to getting the result

let bignum_a:Float = 10/2.5

let bignum_a2:Int = 10/3

let bignum_b:Float = Float(Int(1.2))*10.1

let bignum_c:Int = Int(3.99)

// summary: 3.it need change two number‘s type in the same ,in order to getting the result

//          4.forcing number type need add type symbol in the front of number

let jy = "爱下厨"

let address = ".Jianggan,Hangzhou City,ZheJiang Province,China"

jy + address

let params = (isLoginSuccess:true,name:"tommy",age:25)

let (isLoginSuccess,name,age) = params

let isLginSuccess = params.0

let whats = params.name

let whatsage = params.2

let (isTrue,_,_) = params

if (isTrue)

{

print("login success!")

}

let personArray = ("a","b","c","d")

let aPerson = personArray.0

let bPerson = personArray.1

// summary: 5. Tuples

var value_a:Int

value_a = 1

var imOptionalVariable:Int?

// summary: it‘s equal to nil when the optionalVariable is empty

imOptionalVariable = 56

let name = "Tommy"

var age = Int(name)

if age != nil

{

print("it‘s not empty")

}

else {

print("it‘s empty!")

}

let userage = "25"

var currentAge = Int(userage)

let currentnewAge = Int(userage)

// summary: String toInt use method : Int(string)

if currentAge != nil

{

print("age: \(currentAge)")

print("his age is " + String(currentAge!))

}

if userage .isEmpty

{

print("age: \(userage)")

}else {

print("age :\(userage)")

}

let stringA:String? = "optional_String"

let string2 = "_/stringA"

var stringB = stringA! + string2

stringA

stringA!