- 函数的基本的创建方法及使用
//函数的声明
//有返回值，有参数
func sayHello(name:String?,greenting:String) -> String
{
let result = greenting + (name ?? "Guest")+"!"
return result
}
//有返回值、无参数
func sayWelcome() -> String
{
return "welcome"
}
//无返回值
func endConversation()
{
print("#the contversion is over#")
}
func endConversation1() -> Void
{
print("#the contversion is over#")
}
func endConversation2() -> ()
{
print("#the contversion is over#")
}
//函数的调用
var nickName : String?
nickName = "Nick"
print( sayHello(name: nickName, greenting: "Good morning"))
print( sayWelcome() )
- 有多个返回值的函数
//使用元组让函数返回多个值
func maxminScore ( scores:[Int] ) -> (maxScore:Int,minScore:Int)?
{
if scores.isEmpty {
return nil
}
var curMax = scores[0], curMin = scores[0]
for score in scores[1..<scores.count]{
curMax = max(curMax,score)
curMin = min(curMin,score)
}
return(curMax,curMin)
}
var userScores:[Int]? = [12,220,573,35489,249]
userScores = userScores ?? []
if let result = maxminScore(scores: userScores!){
print("This maximum user score is:\(result.maxScore)")
print("This maximum user score is:\(result.minScore)")
}
- 有默认参数值的函数
//参数的默认值
func sayHai(name:String?, greenting:String = "hello" ,other:String = "how do you do") -> String
{
let result = greenting + (name ?? "Guest")+"!"+other
return result
}
sayHai(name: "bobobo", greenting: "hi")
sayHai(name: "nihao")
sayHai(name: "nihao",other:"how are you")
- 参数可变的函数
一个函数最多只能设置一个可变参数，并且这个可变的参数必须放在整个函数的参数列表的最后的位置；
正常来说函数的参数列表应该为：必须的参数，具有默认值的参数，可变的参数
//参数可变的函数
func add(a:Int,b:Int,others:Int ...) -> Int
{
var result = a+b
for number in others
{
result += number
}
return result
}
var res = add(a: 2 , b: 3)
res = add(a: 2, b: 3, others: 4, 5)
- 函数的参数类型
- 常量参数
swift函数中的参数，默认是不可修改的，这类参数为常量参数 - 变量参数（在swift 3中不被允许）
不管是字典还是数组等类型的参数，在swift的函数中被改变后，传入的参数本身是不会发生变化的，即参数的传递都是值传递；
在swift 3 中要想使用并改变传入的参数，只能用下面的办法，如:
func toBinary( num:Int) -> String
{
var num = num
var result:String = ""
while num != 0 {
result = String( num % 2) + result
num /= 2
}
return result
}
var num = 5
toBinary(num: num)
num //结果还是5
- inout 参数
要想通过函数彻底改变传入的参数的值，需要将参数类型声明为inout类型，如：
func swapTwoInts( a:inout Int ,b:inout Int)
{
let t = a
a = b
b = t
}
var x = 0, y = 100
swapTwoInts(a: &x, b: &y)
x // 100
y //0
函数类型
即函数同时也是一种参数，可以存在一个变量中，其主要应用：-
将一个函数作为一个参数传递到另外一个函数中
func add( a:Int,b:Int) -> Int
{
return a+b
}
let anotherAdd = add
anotherAdd(3,4)
let anotheradd1:(Int,Int)->Int
let anotherSayhello:(String)->()
func changeScores(op:(Int)->Int, scores:inout [Int]){
for i in 0..<scores.count{
scores[i] = op(scores[i])
}
}
func op1(x:Int)->Int{
return Int(sqrt(Double(x))*10)
}
var scores = [34,34,67,89,90]
changeScores(op: op1, scores: &scores)
scores
var arr = Int
for _ in 1...20{
arr.append(Int(arc4random()%100))
}
//sorted 函数默认是升序排序
arr.sorted()
func compareTwoInts(a:Int,b:Int)->Bool
{
return a>b
}
//降序排序
arr.sorted(by: compareTwoInts)
var strArr = ["d","c","df","hdjkfs","dhfj","i"]
strArr.sorted()
func compareTwoString(s1:String,s2:String)->(Bool)
{
return s1.characters.count < s2.characters.count
}
//按字符串长度排序
strArr.sorted(by: compareTwoString)
- 将函数作为返回值返回
主要意义在于解耦，提高代码易读性和易维护性
func tierlMailTee(weight:Int)->Int{
return 1weight
}
func tier2MailTree(weight:Int)->Int{
return 2weight
}
func totalPrice(price:Int,weight:Int) -> Int
{
func chooseMailFeeCalcmethod(weight:Int) -> (Int)->Int
{
return weight <= 10 ?tierlMailTee : tier2MailTree
}
let mailFeeCalc:(Int)->Int = chooseMailFeeCalcmethod(weight: weight)
return mailFeeCalc(weight) + price*weight
}
