//練習一
var explicitFloat:Float = 50
print(explicitFloat)


//練習二
var implicitFloat = 20.0
print("Hello Jim ,I geive you \(implicitFloat) money")


//標記：在if 語句中，條件必須是一個布林表示式——這意味著像if score { ... } 這樣的程式碼將報錯，而不會隱形地
//與 0 做對比。


//可選型別
var optionalString: String? 
print(optionalString == nil)//說明預設的是nil


var optionalString1: String? = ""
print(optionalString1 == nil)//說明""也是佔記憶體的，與nil不同


var optionalString2: String? = "nil"
print(optionalString2 == nil)//說明"nil"是個字串，與nil不同


var optionalString3: String? = "Hello World"
print(optionalString3 == nil)//說明optionalString3有值


//switch
//執行switch 中匹配到的子句之後，程式會退出switch 語句，並不會繼續向下執行，所以不需要在每個子句結尾
//寫break 。
let vegetable = "red pepper"
switch vegetable {
    case "celery":
        print("Add some raisins and make ants on a log.")
    case "cucumber", "watercress":
        print("That would make a good tea sandwich.")
    case let x where x.hasSuffix("pepper"):
        print("Is it a spicy \(x)?")
    default:
        print("Everything tastes good in soup.")
}//刪除default報錯：error: switch must be exhaustive, consider adding a default clause，default不能省略