我們一起聊聊Swift 條件控制和循環
歡迎您閱讀 Mastering Swift 基礎教程，本文我們將介紹 Swift 中的變量、常量和數據類型。如果你尚未安裝 Xcode 和配置 Swift 開發環境，請您先閱讀這篇文章。
接下來，我們啟動 Xcode，然后選擇 "File" > "New" > "Playground"。創建一個新的 Playground 并命名為 "ConditionalsAndLoops"。
if...else
if-else 語句是一種常見的條件控制結構，用于根據條件的真假執行不同的代碼塊。
Swift Code
var temperature = 28
if 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
if...else if...else 語句允許您按順序處理多個條件。
Swift Code
let score = 85
if 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
switch 語句是一種用于處理多個可能情況的流程控制結構。在 Swift 中，switch 語句可以用于處理各種數據類型，包括整數、浮點數、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，無需使用 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
for-in 語句用于遍歷集合（如數組、字典或范圍）的循環結構。
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
*/在以上代碼中，1...5 是一個閉區間運算符，表示一個包括從 1 到 5 的整數范圍。這個范圍包括 1 和 5 兩個端點。
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 循環還支持 where 子句，它可以更好地控制循環代碼何時執行。
Swift Code
for index in 1...5 where index % 2 == 0 {
print("Index is \(index)")
}
/**
Output:
Index is 2
Index is 4
*/while
while 語句是一種用于創建循環的控制流結構，只要給定條件為真，就會反復執行一段代碼塊。
Swift Code
var count = 1
while 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
repeat-while 語句是一種循環結構，類似于 while 循環，不同之處在于 repeat-while 會先執行一次代碼塊，然后在滿足條件的情況下重復執行。
Swift Code
var count = 1
repeat {
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
*/以上代碼中，repeat-while 循環會先執行一次代碼塊，然后檢查條件 count <= 5 是否仍然為真。只要條件為真，就會重復執行代碼塊。這確保了至少會執行一次，即使條件一開始就不滿足。
在 TypeScript 中，目前并沒有對應于 Swift 中 repeat-while 的語法。但可以通過 do-while 循環來實現類似的功能。
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
*/本文我們介紹了 Swift 中 if/else, else if, switch 和 loops 語句等相關的知識。通過與 TypeScript 語法的對比，希望能幫助您更好地理解 Swift 的相關特性。
