欢迎您阅读 Mastering Swift 基础教程，本文我们将介绍 Swift 中的变量、常量和数据类型。如果你尚未安装 Xcode 和配置 Swift 开发环境，请您先阅读这篇文章。
接下来，我们启动 Xcode，然后选择 "File" > "New" > "Playground"。创建一个新的 Playground 并命名为 "ConditionalsAndLoops"。
if-else 语句是一种常见的条件控制结构，用于根据条件的真假执行不同的代码块。
Swift Code
var temperature = 28if temperature > 30 { print("It's a hot day")} else { print("It's not so hot")}// Output: It's not so hotTypeScript Code
let temperature = 28;if (temperature > 30) { console.log("It's a hot day");} else { console.log("It's not so hot");}// Output: "It's not so hot"if...else if...else 语句允许您按顺序处理多个条件。
Swift Code
let score = 85if score >= 90 { print("Excellent!")} else if score >= 80 { print("Good")} else if score >= 70 { print("Average")} else { print("Fail")}// Output: GoodTypeScript Code
const score: number = 85;if (score >= 90) { console.log("Excellent!");} else if (score >= 80) { console.log("Good");} else if (score >= 70) { console.log("Average");} else { console.log("Fail");}// Output: Goodswitch 语句是一种用于处理多个可能情况的流程控制结构。在 Swift 中，switch 语句可以用于处理各种数据类型，包括整数、浮点数、字符串 等。
Swift Code
let dayOfWeek = "Wednesday"switch dayOfWeek {case "Monday": print("Start of the workweek")case "Tuesday", "Wednesday", "Thursday": print("Midweek, work in progress")case "Friday": print("It's Friday, almost there!")case "Saturday", "Sunday": print("Weekend vibes")default: print("Invalid day")}// Output: Midweek, work in progress相比 JavaScript 和 TypeScript，在 Swift case 分支中，无需使用 break 跳出分支。
TypeScript Code
const dayOfWeek: string = "Wednesday";switch (dayOfWeek) { case "Monday": console.log("Start of the workweek"); break; case "Tuesday": case "Wednesday": case "Thursday": console.log("Midweek, work in progress"); break; case "Friday": console.log("It's Friday, almost there!"); break; case "Saturday": case "Sunday": console.log("Weekend vibes"); break; default: console.log("Invalid day");}// Output: "Midweek, work in progress"for-in 语句用于遍历集合（如数组、字典或范围）的循环结构。
Swift Code
for index in 1...5 { print("Index is /(index)")}/** Output: Index is 1 Index is 2 Index is 3 Index is 4 Index is 5 */在以上代码中，1...5 是一个闭区间运算符，表示一个包括从 1 到 5 的整数范围。这个范围包括 1 和 5 两个端点。
TypeScript Code
for (let index = 1; index <= 5; index++) { console.log(`Index is ${index}`);}/** Output: Index is 1 Index is 2 Index is 3 Index is 4 Index is 5 */在 Swift 中 for-in 循环还支持 where 子句，它可以更好地控制循环代码何时执行。
Swift Code
for index in 1...5 where index % 2 == 0 { print("Index is /(index)")}/** Output: Index is 2 Index is 4 */while 语句是一种用于创建循环的控制流结构，只要给定条件为真，就会反复执行一段代码块。
Swift Code
var count = 1while count <= 5 { print("Count is /(count)") count += 1}/** Output: Count is 1 Count is 2 Count is 3 Count is 4 Count is 5 */TypeScript Code
let count: number = 1;while (count <= 5) { console.log(`Count is ${count}`); count++;}/** Output: Count is 1 Count is 2 Count is 3 Count is 4 Count is 5 */repeat-while 语句是一种循环结构，类似于 while 循环，不同之处在于 repeat-while 会先执行一次代码块，然后在满足条件的情况下重复执行。
Swift Code
var count = 1repeat { print("Count is /(count)") count += 1} while count <= 5/** Output: Count is 1 Count is 2 Count is 3 Count is 4 Count is 5 */以上代码中，repeat-while 循环会先执行一次代码块，然后检查条件 count <= 5 是否仍然为真。只要条件为真，就会重复执行代码块。这确保了至少会执行一次，即使条件一开始就不满足。
在 TypeScript 中，目前并没有对应于 Swift 中 repeat-while 的语法。但可以通过 do-while 循环来实现类似的功能。
TypeScript Code
let count: number = 1;do { console.log(`Count is ${count}`); count++;} while (count <= 5);/** Output: Count is 1 Count is 2 Count is 3 Count is 4 Count is 5 */本文我们介绍了 Swift 中 if/else, else if, switch 和 loops 语句等相关的知识。通过与 TypeScript 语法的对比，希望能帮助您更好地理解 Swift 的相关特性。
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