Swift 二 基本运算符 Basic Operators

let b = 10
var a = 5
a = b // 10

• 取余

9 % 4 // 1
-9 % 4 // -1

let three = 3
let minusThree = -three // -3
let plusThree = -minusThree // 3

var a = 1
a += 2 // 3

let name = "world"
if name == "world" {
    print("hello,world")
} else {
    print("I'm sorry \(name)")
}

(1,"zebra") < (2,"apple") // true 1 < 2
(3,"apple") < (3,"bird") // true apple < bird
(4,"dog") == (4,"dog") // true
("blue",-1) < ("purple",1) // true
("blue",false) < ("purple",true) // error bool不能比较

let contentHeight = 40
let hasHeader = true
let rowHeight = contentHeight + (hasHeader ? 50 : 20) // 90

let defaultColorName = "red"
var userDefinedColorName : String? // nil
var colorNameToUse = userDefinedColorName ?? defaultColorName // red

userDefinedColorName = "blue"
colorNameToUse = userDefinedColorName ?? defaultColorName // blue

区间运算

for index in 1...5 {
    print("\(index) times 5 is \(index * 5)")
}
/*
 1 times 5 is 5
 2 times 5 is 10
 3 times 5 is 15
 4 times 5 is 20
 5 times 5 is 25
 */

let names = ["Anna","Alex","Brain","Jack"]
let count = names.count
for i in 0..<count {
    print("Person \(i + 1) is called \(names[i])")
}
/*
 Person 1 is called Anna
 Person 2 is called Alex
 Person 3 is called Brain
 Person 4 is called Jack
 */

for name in names[2...] {
    print(name)
}
/*
 Brain
 Jack
 */

for name in names[...2] {
    print(name)
}
/*
 Anna
 Alex
 Brain
 */