Swift循环控制

for - in 循环

• 遍历序列，如一个范围内的数字，数组中的元素或者字符串中的字符

for i in 0...3 {
    print(i)
}

for c in "Hello,world" {
    print(c)
}

let names = ["zhangsan","lisi","wangwu"]
for name in names {
    print(name)
}

for - in 遍历字典

• 当字典遍历时，每一个元素都返回一个（key、value）元组，你可以在for - in 循环中使用显式命名常量来分解（key、value）元组成员。

let numberOfLegs = ["spider":8, "ant":6, "cat":4]
for (animalName, legCount) in numberOfLegs {
    print("\(animalName) has \(legCount) legs")
}

for t in numberOfLegs {
    print("\(t.0) has \(t.1) legs")
}

for - in 循环

• 如果你不需要序列的每一个值，你可以使用下划线来取代遍历名以忽略值

let base = 3
let power = 5
var answer = 1
for _ in 1...power {
    answer *= base
}
print("\(base) to the power of \(power) is \(answer)")

运行结果为：
3 to the power of 5 is 243

for - in 分段区间

• 使用 stride(from:to:by:) 函数来跳过不想要的标记（开区间）
• 闭区间也同样适用，使用 stride(from:through:by:) 即可。

let minuteInterval = 5
for tickMark in stride(from: 0, to: 50, by: minuteInterval) {
    print(tickMark)
}

运行结果为：
0
5
10
15
20
25
30
35
40
45

闭区间

let minuteInterval = 5
for tickMark in stride(from: 0, through: 50, by: minuteInterval) {
    print(tickMark)
}

运行结果为：
0
5
10
15
20
25
30
35
40
45
50

while 循环

• repeat - while 循环

var count = 0
repeat {
    print(count)
    count += 1
} while count < 5

运行结果为：
0
1
2
3
4