[Day08] swift & kotlin 入门篇！(6) 流程控制-循序,选择,重复

流程控制

基础语法过後就是流程控制了
流程控制结束就可以进入快乐的开发阶段搂～
流程控制是程序设计中非常重要的概念
甚至可以说所有功能几乎都是靠流程控制拼凑出来的

流程控制三大招 - 循序选择重复

swift

// 循序- 执行步骤是一步一步承续下来
print("第一步")
print("第二步")
print("第二步")

// 选择 if
let a = 10
let b = 15
if a > b {
    print("if a 大 ")
} else {
    print("if b 大 ")
}

// 选择 switch
switch a {
    case 10:
        print("switch a 是 10")
    case 10...15:// 很多语言的switch是无法做到区间判断的喔
        print("switch a 是 10 到 15之间的一个数")
    default:
        print("switch a 是 啥？")
}

// 重复
let list = ["10", "11", "12", "13","14", "15"]
for (val)  in list {
    print("list value is \(val) ")
}
for (val)  in 5...10 {
    print("value is \(val) ")
}
let myList =  ["user1": 10, "user2": 20, "user3": 30]
for (ind, val)  in myList{
    print("index is \(ind) value is \(val) ")
}
-------- 控制台输出 ------------
第一步
第二步
第二步
if b 大 
switch a 是 10
list value is 10 
list value is 11 
list value is 12 
list value is 13 
list value is 14 
list value is 15 
value is 5 
value is 6 
value is 7 
value is 8 
value is 9 
value is 10 
index is user3 value is 30 
index is user1 value is 10 
index is user2 value is 20

Swift 有个比较少见的 Range 类
是在其他语言比较少看到的
5...10 表 5~10 其实蛮直觉又好用的
期待之後实务上的应用

另外 switch case 的区间判断也蛮特别的
该使用if or switch ???
让我们後面再找范例说明

kotlin

fun main() {
    // 循序- 执行步骤是一步一步承续下来
    println("第一步")
    println("第二步")
    println("第二步")

    // 选择 if
    val a = 10
    val b = 15
    if (a > b) {
        println("if a 大 ")
    } else {
        println("if b 大 ")
    }

    // 选择 when
    when (a) {
        10 -> println("when a 是 10")
        in 10..15 -> println("when a 是 10 到 15之间的一个数") // kotlin range 是.. 而swift用...
        else -> println("when a 是 啥？")
    }

    // 重复
    val list = mutableListOf("10", "11", "12", "13","14", "15")
    for (value  in list) {
        println("只取 value is $value ") 
    }
    for ((ind, value)  in list.withIndex()) {
        println("index is $ind list value is $value ")
    }
    for ((_, value)  in (5..10).withIndex()) {
        println("value is $value ")
    }
    
    val myList =  mutableMapOf("user1" to 10, "user2" to 20, "user3" to 30)
    for ((ind, value)  in myList){
        println("map index is $ind value is $value ")
    }
}
-------- 控制台输出 ------------
第一步
第二步
第二步
if b 大 
when a 是 10
只取 value is 10 
只取 value is 11 
只取 value is 12 
只取 value is 13 
只取 value is 14 
只取 value is 15 
index is 0 list value is 10 
index is 1 list value is 11 
index is 2 list value is 12 
index is 3 list value is 13 
index is 4 list value is 14 
index is 5 list value is 15 
value is 5 
value is 6 
value is 7 
value is 8 
value is 9 
value is 10 
map index is user1 value is 10 
map index is user2 value is 20 
map index is user3 value is 30

kotlin在for跑list上需特别注意几个关键字
list.indices 会只取出 index
list.withIndex() 同时取出 index 及 value
而map跑for时本身就会带出index与value