12.1_8_7_5
1.21875e1 //10的一次方
0xC.3p0
let integerPi = Int(3.1415) //強制截斷
元祖(多個值組合成一個復合值)
let http404Error = (404,"Not Found")
let (justTheStatusCode, _) = http404Error//忽略參數可以用 _
let (aInt,aString) = http404Error
print("the first item is \(http404Error)")
數據類型轉化
let number = "123"
let numToStr = Int(number)
let three = 3
let pointOneFourOneFiveNine = 0.14159
let pi = Double(three) + pointOneFourOneFiveNine
// pi 等于 3.14159，所以被推測為 Double 類型
