一.for循环
for－in
实例1：
for index in 1...5{
print("\(index)times 5 is \(index * 5)")
}结果：
1times 5 is 5 2times 5 is 10 3times 5 is 15 4times 5 is 20 5times 5 is 251...5表示：［1，5］大于等于1且小于等于5
如果括号内不使用index，可以用_代替：
var a = 5
for _ in 1...5{
a += 1
}
print("\(a)")结果：
10
遍历数组：
let nameArr = ["Lili","Marry","xiaoming"]
for name in nameArr {
print("Hello,\(name)!")
}
结果：
Hello,Lili! Hello,Marry! Hello,xiaoming!
遍历字典：
let ageDict = ["Lili":9,"Marry":10,"xiaoming":12]
for (name,age) in ageDict {
print("\(name) is \(age)!")
}结果：
Marry is 10! Lili is 9! xiaoming is 12!由于字典是无序的，所以结果不一定按顺序输出。
二。while循环
语法：
while condition {
statements
}
举例：
//唉，举例无能
var a = 10
while a>0 {
a = a-2
}
print(a)结果：0
原来的do...while循环在此处替换成了repeat...while循环。（不举例了）
三。switch
实例：
let someCharacter: Character = "z"
switch someCharacter {
case "a":
print("The first letter of the alphabet")
case "z":
print("The last letter of the alphabet")
default:
print("Some other character")
}结果：
The first letter of the alphabet
＊ 注意：与C和Objective_C不同，3.0的swift中switch语句的case中不再需要使用break跳出switch语句，匹配条件后即跳出Switch语句，同时，switch中的default是必须的。
虽然break在switch中不再是必须的，但是由于switch中的case／default中语句不允许有空语句，此时，我们可以使用break跳出语句。
例如：
let anotherCharacter: Character = "a"
switch anotherCharacter {
case "a": // Invalid,the case has an empty body
case "A":
print("The letter A")
default:
print("Not the letter A")
}
if let integerValue = possibleIntegerValue {
print("The integer value of \(numberSymbol) is \(integerValue).")
} else {
print("An integer value could not be found for \(numberSymbol).")
}case "a":是无效的，这将导致程序报错： 'case' label in a 'switch' should have at least one executable statement。
再看下面这个例子
let numberSymbol: Character = "三" // Chinese symbol for the number 3
var possibleIntegerValue: Int?
switch numberSymbol {
case "1","١","一","๑":
possibleIntegerValue = 1
case "2","٢","二","๒":
possibleIntegerValue = 2
case "3","٣","三","๓":
possibleIntegerValue = 3
case "4","٤","四","๔":
possibleIntegerValue = 4
default:
break
}
if let integerValue = possibleIntegerValue {
print("The integer value of \(numberSymbol) is \(integerValue).")
} else {
print("An integer value could not be found for \(numberSymbol).")
}
// Prints "The integer value of 三 is 3."此时，default中的可能性很多，我们可能不再需要设置一个possibleIntegerValue的值，此时就可以使用break跳出switch语句。
间隔匹配：
例如：
let grade = 67
switch grade {
case 0...59:
print("不及格")
case 60...79:
print("及格")
case 80...89:
print("良好")
case 90...100:
print("优秀")
default:
break
}
//输出：及格
元祖（Tuples）匹配：
let somePoint = (1,1)
switch somePoint {
case (0,0):
print("(0,0) is at the origin")
case (_,0):
print("(\(somePoint.0),0) is on the x-axis")
case (0,_):
print("(0,\(somePoint.1)) is on the y-axis")
case (-2...2,-2...2):
print("(\(somePoint.0),\(somePoint.1)) is inside the Box")
default:
print("(\(somePoint.0),\(somePoint.1)) is outside of the Box")
}
// Prints "(1,1) is inside the Box"
下划线（_）也称为通配符，可以匹配任何可能的值。
值绑定：
let anotherPoint = (2,0)
switch anotherPoint {
case (let x,0):
print("on the x-axis with an x value of \(x)")
case (0,let y):
print("on the y-axis with a y value of \(y)")
case let (x,y):
print("somewhere else at (\(x),\(y))")
}
// Prints "on the x-axis with an x value of 2"
where：Switch中还可以使用where来设置附加条件
例如：
let yetAnotherPoint = (1,-1)
switch yetAnotherPoint {
case let (x,y) where x == y:
print("(\(x),\(y)) is on the line x == y")
case let (x,y) where x == -y:
print("(\(x),\(y)) is on the line x == -y")
case let (x,y):
print("(\(x),\(y)) is just some arbitrary point")
}
// Prints "(1,-1) is on the line x == -y"
控制转移语句：
1.continue；
2.break（不再重复说明）;
3.fallthrough;
4.return.
5.throw。
continue:跳出当前循环，执行下一次循环。
例如：
let puzzleInput = "great minds think alike"
var puzzleOutput = ""
for character in puzzleInput.characters {
switch character {
case "a","e","i","o","u"," ":
continue
default:
puzzleOutput.append(character)
}
}
print(puzzleOutput)
// Prints "grtmndsthnklk"
fallthrough:条件匹配成功后，继续执行后面的语句。
例如：
let integerToDescribe = 5
var description = "The number \(integerToDescribe) is"
switch integerToDescribe {
case 2,3,5,7,11,13,17,19:
description += " a prime number,and also"
fallthrough
default:
description += " an integer."
}
print(description)
// Prints "The number 5 is a prime number,and also an integer."
return：跳出整个循环与语句。 原文链接：https://www.f2er.com/swift/323314.html