if-else while for

swift系列课程

if-else

let age = 4
if age >= 22 {
}
else if age >=18 {
}
else {
}

• if后面的条件都可以省略小括号
• 条件后面的大括号不可以省略
• if后面的条件只能是Bool类型

while

var num = 5
while num > 0 {
       print("num is \(num)")
       num -= 1
}

var num = -1
repat {
         print("num is \(num)")
} while num >0//打印了一次

• repeat-while 相当于c语言中的do-while
• 这里不用num-- ，是因为从Swift3开始去掉了自增（++）,自减（--）运算符

for

• 闭区间运算符：a...b, a<=取值<=b

let names = ["kkk","bbb","ccc","ddd"]
for i in 0...3 {
      print(names[I])
}

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

let a = 1
var b = 2
for i in a...b {
     print(names[I])
}

注释

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