Introduction to swift practice output Chapter 5 Part 2

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.

for-in statement enumeration of sequence elements

chapter5.swift

let array = [1,2,3]
for element in array {
    print(element)
}

Dictionary

chapter5.swift

let dictionary = ["a": 1, "b": 2]
for (key,value) in dictionary {
    print("Key: \(key), vlue: \(value)")
}

while statement repeats according to continuation conditions

chapter5.swift

var f = 1
while f < 4 {
    print(f)
    f += 1
}

repeat while statement

Since the while statement evaluates the conditional expression before execution, it may never be executed. Therefore, if you want to repeat it more than once regardless of the success or failure of the conditional expression, use repeat whie.

chapter5.swift

var t = 1
repeat {
    print(t)
    t += 3
}
while t < 1

Suspended during execution

The break statement ends the entire repeating statement.

chapter5.swift

var containsTwo = false
let garray = [1,2,3]

for element in garray {
    if element == 2 {
        containsTwo = true
        break
    }
    print("element:\(element)")
}
print("containsTwo:\(containsTwo)")

The continue statement suspends only the current processing and continues the subsequent processing.

chapter5.swift

var odds = [Int]()
let rarray = [1,2,3,4,5,6]

for element in rarray {
    if element % 2 == 1 {
        odds.append(element)
        continue
    }
    print("even:\(element)")
}
print("odds:\(odds)")
}

Defer statement for delayed execution

defer statement: Processing when leaving the scope

chapter5.swift

var count = 0

func someFUNTIONS() -> Int{
    defer {
        count += 1
    }
    return count
}
print(someFUNTIONS())
print(someFUNTIONS())
print(count)

Evaluation based on the structure and nature of pattern matching values

swift has the concept of a pattern that expresses the structure and properties of a value Waiting for a pattern is to check if the value matches a specific pattern.

Expression pattern ~ = Evaluation by operator

chapter5.swift

let integer = 6

switch integer {
case 6:
    print("match: 6")
    
case 5...10:
    print("match: 5...10")
    
default:
    print("default")
}

Value binding Evaluation with value substitution

chapter5.swift

let values = 3

switch values {
case let matchValue :
    print(matchValue)
}

Evaluation of the presence or absence of an optional type value

chapter5.swift

let values = 3
let optionalD = Optional(4)
switch optionalD{
case let f?:
    print(f)
    
default:
    print("nil")
}

}

Enumeration type case pattern Evaluation of match with case

chapter5.swift

enum Hemisphere {
    case northern
    case southern
}

let hemisphere = Hemisphere.southern
//let hemisphere = Optional(Hemisphere.southern)
switch hemisphere {
case .northern:
    print("match: .northern")
case .southern:
    print("match: .southern")
//case nil:
//    print("nil")
}

enum Color {
    case rgb(Int,Int,Int)
    case cmyk(Int,Int,Int,Int)
}

let color = Color.rgb(100, 200, 230)
switch color {
case .rgb(let r, let h, let j):
print(".rgb: (\(r), \(h), \(j))")
case .cmyk(let k,let y, let u, let o):
print(" .cmyk: (\(k),\(y),\(u),\(o))")

}

Type casting pattern by is operator Evaluation by type judgment

chapter5.swift

let any: Any = "fafafa"
switch any {
case is String:
    print("match: String")
case is Int:
    print("match: Int")
default:
    print("default")
}

}

Type casting pattern by as operator Evaluation by type casting

chapter5.swift

let anys : Any = "1"
switch anys {
case let string as String:
    print("match: string(\(string))")
case let int as Int:
    print("match: int(\(int))")
default:
    print("default")
}

Where pattern matching can be used if statement

chapter5.swift

let fff = 9
if case 1...10 = fff {
    print("yes")
}

//guard statement
func someFunc() {
    let value = 9
    guard case 1...10 = value else {
        return
    }
    print("yes")
}
someFunc()

//for in statement
let harray = [1,2,3,4,5,6]
for case 2...5 in harray {
    print("2 or more and 5 or less")
}

while statement

chapter5.swift

var nextValue = Optional(1)
while case let value? = nextValue {
    print("value:\(value)")
    
    if value >= 8 {
        nextValue = nil
    } else {
        nextValue = value + 1
    }
}