Swift: 03-流程控制

//if 后面只能是Bool类型
let age = 4
if age >= 22 {
    print("Get married")
} else if age >= 18 {
    print("Being a adult")
} else if age >= 7 {
    print("go to school")
} else {
    print("just a child")
}


var num = 5
while num > 0 {
    print("num is \(num)")
    num -= 1
}
//从 Swift3开始，去除了自增（++），自减（--）运算符

var num2 = -1
repeat {
    print("num2 is \(num2)")
} while num > 0

let names = ["Anna", "Alex", "Brian", "jack"]
for i in 0...3 {
    print(names[i])
}

for name in names[1...3] {
    print(name)
}

let range = 1...3
for i in range {
    print(names[i])
}

//i 默认是let，有需要时可以申明为var
for var i in 1...3 {
    i += 5
    print(i)
}

for _ in 1...3 {
    print("for")
}
//半开区间：a..<b, 意思是a<=取值<b
for i in 1..<5 {
    print(i)
}

//:#### for - 区间运算符用在数组上
 
let names1 = ["Anna", "Alex", "Brian", "Jack"]
for name in names1[3...3] {
    print(name)
} //Jack
 

//单侧区间：让区间朝一个方向尽可能的远, 在数组里面，是有限定的，从0开始，最大到底数组的长度，最后一个字符
for name in names[2...] {
    print(name)
} //Brian, Jack

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

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


//与上面rang放到数组里面形成对比，在外面范围会更大
let rang = ...5
print(rang.contains(7))
print(rang.contains(3))
print(rang.contains(-3))


//:#### 区间类型
let range1: ClosedRange<Int> = 1...3 //闭区间
let range2: Range<Int> = 1..<3 //半开区间
let range3: PartialRangeThrough<Int> = ...5


//字符，字符串也能使用区间运算符，但默认不能用在for-in中
let stringRange1 = "cc"..."ff"
print(stringRange1.contains("cb")) //false
print(stringRange1.contains("dz")) //true
print(stringRange1.contains("fg")) //false

let stringRange2 = "a"..."f"
print(stringRange2.contains("d")) //true
print(stringRange2.contains("h")) //false


let str = "a" //"a"默认为string类型
let char: Character = "a" //如果想申明为字符类型，必须要指定类型才行

// \0到～囊括里所有可能要用到的ASCII字符
let characterRange: ClosedRange<Character> = "\0"..."~"
print(characterRange.contains("G")) //true


//:#### 带间隔的区间
let hours = 11
let hourInterval = 2
// tickMark 的取值：从4开始，累加2，不超过11
for tickMark in stride(from: 4, through: hours, by: hourInterval) {
    print(tickMark)
} // 4 6 8 10


//switch
var number = 1
switch number {
case 1:
    print("number is 1")
    break
case 2:
    print("number is 2")
    break
default:
    print("number is other")
    break
} //number is 1
//case, default后面不能写大括号{}

var number2 = 1
switch number2 {
case 1:
    print("number is 1");
case 2:
    print("number is 2");
default:
    print("number is other");
}
//默认可以不写break，并不会贯穿到后面的条件


//fallthrough
//使用fallthrough可以实现贯穿效果
//注意：switch必须要保证能处理所有情况
 
var number3 = 1
switch number3 {
case 1:
    print("number is 11")
    fallthrough
case 2:
    print("number is 22")
default:
    print("number is other")
}

//case，default后面至少有一条语句
//如果不想做任何事情，加个break即可
var number4 = 1
switch number4 {
case 1:
    print("number is 11")
    fallthrough
case 2:
    print("number is 22")
default:
    break
}

//如果可以保证已处理所有情况，也可以不必使用default
enum Answer {case right, wrong}
let answer = Answer.right
switch answer {
case Answer.right:
    print("right")
case Answer.wrong:
    print("wrong")
} //right

//或者如果可以确定answer是Ansewer类型，可以省略Answer
switch answer {
case .right:
    print("right")
case .wrong:
    print("wrong")
} //right

//复合条件
//switch也可以支持Character, String类型
let string = "Jack"
switch string {
case "Jack":
    fallthrough
case "Rose":
    print("Right person")
default:
    break
} //Right person

//上面的逻辑也可以写成下面这样
switch string {
case "Jack","Rose":
    print("Right person")
default:
    break
} //Right person

//如果是字符需要指定类型 Character
let character: Character = "a"
switch character {
case "a","A":
    print("The letter A")
default:
    print("Not the letter A")
}


//区间匹配
let count = 62
switch count {
case 0:
    print("none")
case 1..<5:
    print("a few")
case 5..<12:
    print("several")
case 12..<100:
    print("dozens of")
case 100..<1000:
    print("hundreds of")
default:
    print("many")
} //dozens of


//元组匹配
//可以使用下划线 _ 忽略某个值
//关于case匹配问题，属于模式匹配（Pattern Matching）范畴，后面会再次详细展开讲解
let point = (1, 1)
switch point {
case (0, 0):
    print("the origin")
case (_, 0):
    print("on the x-axis")
case (0, _):
    print("on the y-axis")
case (-2...2, -2...2):
    print("inside the box")
default:
    print("outside of the box")
} //inside the box


//值绑定
//let也可以换成var
let point2 = (2, 0)
switch point2 {
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 an y value of \(y)")
case let (x, y):
    print("somewhere else at (\(x), \(y))")
} //on the x-axis with an x value of 2


//where
let point3 = (1, -1)
switch point3 {
case let(x, y) where x==y:
    print("on the line x==y")
case let(x, y) where x == -y:
    print("on the line x==-y")
case let(x, y):
    print("(\(x), \(y)) is just some arbitrary point")
} // on the line x == -y

//将所有正数加起来
var numbers = [10, 20, -10, -20, 30, -30]
var sum = 0
for num in numbers where num > 0 {
    sum += num;
}
print("sum is \(sum)")//sum is 60

//标签语句
//可以标记某一个for循环，然后针对性的指定终止某个循环
outer: for i in 1...4 {
outer1:for k in 1...4 {
        if k == 3 {
            continue outer1
        }
        if i == 3 {
            continue outer
        }
        print("i == \(i), k == \(k)")
    }
}