// 演练一:
let a = 10
// 错误写法:
//if a {
// print("a")
//}
// 正确写法
if a > 9 {
print(a)
}
// 演练二:
let score = 87
if score < 60 {
print("不及格")
} else if score <= 70 {
print("及格")
} else if score <= 80 {
print("良好")
} else if score <= 90 {
print("优秀")
} else {
print("完美")
}
// 演练三:
// 这个是可选类型,因为只有声明成可选类型后,才可以判断是否为空
// 可选类型会在后续讲解,可先了解即可
let view : UIView? = UIView()
// 判断如果view有值,则设置背景
// 错误写法
//if view {
// view.backgroundColor = UIColor.red
//}
if view != nil {
view!.backgroundColor = UIColor.red
}
var a = 10
var b = 50
var result = a > b ? a : b
print(result)
guard 条件表达式 else {
// 条换语句
break
}
语句组
例子
var age = 18
func online(age : Int) -> Void {
guard age >= 18 else {
print("回家去")
return
}
print("可以上网")
}
online(age)
let sex = 0
switch sex {
case 0 :
print("男")
case 1 :
print("女")
default :
print("其他")
}
let sex = 0
switch sex {
case 0, 1:
print("正常人")
default:
print("其他")
}
let sex = 0
switch sex {
case 0:
fallthrough
case 1:
print("正常人")
default:
print("其他")
}
let f = 3.14
switch f {
case 3.14:
print("π")
default:
print("not π")
}
let m = 5
let n = 10
var result = 0
let opration = "+"
switch opration {
case "+":
result = m + n
case "-":
result = m - n
case "*":
result = m * n
case "/":
result = m / n
default:
result = 0
}
print(result)
let score = 88
switch score {
case 0..<60:
print("不及格")
case 60..<80:
print("几个")
case 80..<90:
print("良好")
case 90..<100:
print("优秀")
default:
print("满分")
}