Swift Learning (3) - Basic Operators (Fully Ver.)

let b = 10
var a = 5
a = b  // a现在就等于b的值，10
print("将b的值赋给a，现在a的值为：\(a)")
---
output: 将b的值赋给a，现在a的值为：10

var (x, y) = (2, 5)  // 现在x等于2，y等于5
print("元组(2, 5)被分解后，现在x等于：\(x)，y等于：\(y)")
---
output: 元组(2, 5)被分解后，现在x等于：2，y等于：5

// if x = y {
     // 此结构错误，因为x = y并不返回任何值，报错Use of '=' in a boolean context, did you mean '=='?
// }

if x == y {
    // 此结构正常不报错
}

print("1 + 2等于：", 1 + 2)  // 等于3
print("5 - 3等于：", 5 - 3)  // 等于2
print("2 * 3等于：", 2 * 3)  // 等于6
print("10.0 / 2.5等于：", 10.0 / 2.5)  // 等于4.0
---
output: 1 + 2等于： 3
5 - 3等于： 2
2 * 3等于： 6
10.0 / 2.5等于： 4.0

print("Hello " + "World!")  // 等于“Hello World!”
---
output: Hello World!

print("9 % 4的结果是：\(9 % 4)")  // 等于1
---
output: 9 % 4的结果是：1

print("-9 % 4的结果是：\(-9 % 4)")  // 等于-1
---
output: -9 % 4的结果是：-1

print("9 % -4的结果是：\(9 % -4)，与9 % 4的结果相同。")
---
output: 9 % -4的结果是：1，与9 % 4的结果相同。

let three = 3
let minusThree = -three  // minusThree等于-3
let plusThree = -minusThree  // plusThree等于3，即“负负得正”
print("负负得正的结果是：\(plusThree)")
---
output: 负负得正的结果是：3

let minusSix = -6
let alsoMinusSix = +minusSix
print("正号运算符啥都不会改变，所以alsoMinusSix的值为：\(alsoMinusSix)")
---
output: 正号运算符啥都不会改变，所以alsoMinusSix的值为：-6

var c = 2
c += 2
print("c经过组合加运算后的值是：\(c)")  // c现在是3
---
output: c经过组合加运算后的值是：4

print("1等于1：\(1 == 1)")  // true
print("2不等于1：\(2 != 1)")  // true
print("2大于1：\(2 > 1)")  // true
print("1小于2：\(1 < 2)")  // true
print("1大于等于1：\(1 >= 1)")  // true
print("2小于等于1：\(2 <= 1)")  // false
---
output: 1等于1：true
2不等于1：true
2大于1：true
1小于2：true
1大于等于1：true
2小于等于1：false

let name = "Jensen"
if name == "world" {
    print("Hello, World!")
} else {
    print("I'm sorry \(name), but I don't recognize you.")
}
---
output: I'm sorry Jensen, but I don't recognize you.

print("元组比较1：\((1, "zebra") < (2, "apple"))")  // true  因为1小于2，所以(1, "zebra") < (2, "apple")，虽然"zebra" > "apple"，但对最后的结果没有影响
print("元组比较2：\((3, "apple") < (3, "bird"))")  // true  当第一个元素相同时，元组的第二个元素会进行比较
print("元组比较3：\((4, "dog") == (4, "dog"))")  // true
---
output: 元组比较1：true
元组比较2：true
元组比较3：true

print("String和Int类型元素是可以被比较的：\(("blue", -1) < ("purple", 1))")  // 正常，比较的结果为true
//("blue", false) < ("purple", true)  // 错误，因为 < 不能比较布尔类型值，若取消注释，则报错Binary operator '<' cannot be applied to two '(String, Bool)' operands
---
output: String和Int类型元素是可以被比较的：true

let question = 3 > 2
let answer1 = 3, answer2 = 2
print("三元运算符的结果：\(question ? answer1 : answer2)")  // 三元运算符

if question {
    print("answer1的结果是：\(answer1)")
} else {
    print("answer2的结果是：\(answer2)")
}
---
output: 三元运算符的结果：3
answer1的结果是：3

let contentHeight = 40
let hasHeader = true
let rowHeight = contentHeight + (hasHeader ? 50 : 20)  // rowHeight现在是90
print("rowHeight现在的值是：\(rowHeight)")
---
output: rowHeight现在的值是：90

let contentHeights = 40
let hasHeaders = true
var rowHeights = contentHeights
if hasHeaders {
    rowHeights += 50
    print("hasHeaders = True, rowHeights: \(rowHeights)")
} else {
    rowHeights += 20
    print("hasHeaders = False, rowHeights: \(rowHeights)")
}
---
output: hasHeaders = True, rowHeights: 90

var d: Int? = 3
let e: Int? = nil
print("空合运算符的原始表达的结果：\((d != nil ? d! : e)!)")  // d != nil ? d! : e
---
output: 空合运算符的原始表达的结果：3

let defaultColorName = "red"
var userDefinedColorName: String?
var colorNameToUse = userDefinedColorName ?? defaultColorName  // userDefinedColorName的值为Nil，所以colorNameToUse的值为“red”
print("colorNameToUse的颜色是：\(colorNameToUse)")
---
output: colorNameToUse的颜色是：red

userDefinedColorName = "green"
colorNameToUse = userDefinedColorName ?? defaultColorName
print("colorNameToUse的颜色是：\(colorNameToUse)")  // userDefinedColorName非空，因此colorNameToUse的值为“green”
---
output: colorNameToUse的颜色是：green

for index in 1...5 {
    print("\(index) * 5 = \(index * 5)")
}
---
output: 1 * 5 = 5
2 * 5 = 10
3 * 5 = 15
4 * 5 = 20
5 * 5 = 25

let names = ["Jensen", "Alex", "Davis", "Jerry"]
let count = names.count
for i in 0..<count {
    print("第\(i + 1)个人叫\(names[i])")
}
---
output: 第1个人叫Jensen
第2个人叫Alex
第3个人叫Davis
第4个人叫Jerry

for name in names[2...] {
    print("names[2...], ", name)
}

for name in names[...2] {
    print("names[...2], \(name)")
}
---
output: names[2...],  Davis
names[2...],  Jerry
names[...2], Jensen
names[...2], Alex
names[...2], Davis

for name in names[..<2] {
    print("names[..<2], \(name)")
}
---
output: names[..<2], Jensen
names[..<2], Alex

let range = ...5
print("range.contains(7): \(range.contains(7))")  // false
print("range.contains(4): \(range.contains(4))")  // true
print("range.contains(-1): \(range.contains(-1))")  // true
---
output: range.contains(7): false
range.contains(4): true
range.contains(-1): true

let allowedEntry = false
if !allowedEntry {  // 当allowedEntry为false，即!allowedEntry为true时，运行代码块
    print("ACCESS DENIED")  // 输出“ACCESS DENIED”
}
---
output: ACCESS DENIED

let enteredDoorCode = true
let passedRetinaScan = false
if enteredDoorCode && passedRetinaScan {  // passedDoorCode的值是false，所以整个表达式的值也是false
    print("Welcome!")
} else {
    print("ACCESS DENIED")  // 输出"ACCESS DENIED"
}
---
output: ACCESS DENIED

let hasDoorKey = false
let knowsOverridePassword = true
if hasDoorKey || knowsOverridePassword {  // knowsOverridePassword的值是true，所以整个表达式的值是true
    print("Welcome!")  // 输出“Welcome!”
} else {
    print("ACCESS DENIED")
}
---
output: Welcome!

if enteredDoorCode && passedRetinaScan || hasDoorKey || knowsOverridePassword {
    print("Welcome!")  // 输出“Welcome!”
} else {
    print("ACCESS DENIED")
}
---
output: Welcome!

if (enteredDoorCode && passedRetinaScan) || hasDoorKey || knowsOverridePassword {
    print("Welcome!")  // 输出“Welcome!”
} else {
    print("ACCESS DENIED")
}
---
output: Welcome!