Introduction to swift practice output Chapter5

Control syntax

Conditional branching, repetition, delayed execution, pattern matching Syntax that controls the execution flow of a program. There are conditional branching and repetition in the control of the control flow, and they can be combined and executed freely.

branch depending on the success or failure of the if statement condition

chapter5.swift

let value = 5

if value <= 4 {
    print("value is 4 or less")
}else {
    print("value is 5 or more")
}

if let statement Branch depending on the presence or absence of a value

Optional types are data types that allow variables to be assigned nil, while non-optional types cannot be assigned nil. Optional variables have a "?" Or "!" At the end of the data type.

chapter5.swift

let optionalA = Optional(1)

if let a = optionalA {
    print("value is\(a)is")
}else {
    print("Value does not exist")
}

let optionalB = Optional("b")
let optionalC = Optional("c")

if let b = optionalB, let c = optionalC{
    print("value is\(b)When\(c)you know")
}else {
    print("Absent")
}

guardl statement Branch that leaves early when conditions are not met

The guard statement is a syntax that describes what to do if the conditions are not met. If the condition is not met, it is necessary to write a process to end the method, end the iterative process, or exit the scope.

Code that exits processing when the condition is not met using the guard statement

chapter5.swift

//guard conditional expression else{
//Statement executed when the conditional expression is false
//You need to exit to the scope statement where the guard statement is written
//}

func someFunction() {
    let value = -1
    
    guard value >= 0 else {
        print("Value less than 0")
        return
    }
    print(value)
}
someFunction()

Forced exit from the scope of the guard statement

chapter5.swift

func printIfPositive(_ a: Int) {
    guard a > 0 else {
        return
    }
    print(a)
}
printIfPositive(6)

Access to variables and constants declared in the guard statement

What is the difference between a guard let statement and an if let statement? Variables and constants declared in the guard let statement can be used after the guard let statement.

chapter5.swift

func someFONCTION() {
    let a :Any = 3
    
    guard let int = a as? Int else {
        print("a is not an Int type")
        return
    }
    print("The value is of type Int\(int)is")
}
someFONCTION()

func checkInt(num:Int) {
    guard num >= 0 else {
        print("It's a minus")
        return
    }
    print("Is a plus")
}
 
checkInt(num:-10)
checkInt(num:10)

Switch statement Branch by multiple pattern matching

chapter5.swift

let r = -1
switch  r {
case Int.min ..< 0:
    print("r is a negative number")
    
case 1 ..< Int.max:
    print("r is a positive number")
default:
    print("a is 0")
}

Checking the completeness of the case

chapter5.swift

enum SomeEnum {
    case foo
    case bar
    case baz
}

let foo = SomeEnum.foo

switch foo {
case .foo:
    print(".foo")
    
case .bar:
    print(".bar")
    
case .baz:
    print(".baz")

}

where keyword Add conditions that match the case

chapter5.swift

let optionalP: Int? = 12

switch optionalP {
case .some(let a) where a > 10:
    print("Value greater than 10\(a)Exists")
default:
    print("Value does not exist or is less than 10")
}

let g = 1

switch g {
case 1:
    print("Will be executed")
    break
    print("Not executed")
default:
    break
}