## 控制流（Control Flow）
推荐循环使用`for-in`表达式，而不使用`for-condition-increment`表达式。
推荐做法：
~~~
for _ in 0..<3 {
println("Hello three times")
}
for (index, person) in enumerate(attendeeList) {
println("\(person) is at position #\(index)")
}
~~~
不推荐做法：
~~~
for var i = 0; i < 3; i++ {
println("Hello three times")
}
for var i = 0; i < attendeeList.count; i++ {
let person = attendeeList[i]
println("\(person) is at position #\(i)")
}
~~~
