Conditional judgment (while loop & for & switch loop & if else judgment)

if-else

let age = 4
if age >= 22 
{
    
  print("Get married")
  
}else if age >= 18
{
    
  print("Being a adult")
  
}else if age >= 7
{
    
  print("Go to school")
  
} else
{
    
  print("Just a child")
}
/* 1.if The following conditions can omit the parentheses  2. The brace after the condition can't be omitted  */

if The latter condition can only be Bool type 

while

var num = 5
while num > 0 
{
    
  print("num is \(num)")
  num -= 1
} //  Print the 5 Time 

var num = -1
repeat 
{
    
  print("num is \(num)")
} while num > 0 //  Print the 1 Time 

1.repeat-while amount to C In language do-while
2. Here there is no num-- , Because from Swift3 Start , Remove the self increasing （ ++ ）、 Self reduction （ -- ） Operator 

for

Closed interval operators ：a…b, a <= Value <= b

let names = ["Anna","Alex","Brian","Jack"]
for i in 0...3 
{
    
  print(names [i])
} // Anna Alex Brian "Alex", "Brian", "Jack"]

let range = 1...3
for i in range
 {
    
  print(names [i])
 } // Alex Brian Jack

let a = 1
var b = 2
for i in a...b 
{
    
  print(names [i])
} // Alex Brian



for i in a...3 
{
    
  print(names [i])
} // Alex Brian Jack

// i The default is let, If necessary, it can be declared as var
for var i in 1...3
{
    
  i += 5
  print(i)
} // 6 7 8

for _ in 1...3 
{
     
   print("for")
} //  Print the 3 Time 

Semi open interval operator ：a…<b, a <= Value < b

for i in 1..<5
{
    
  print(i)
} // 1 2 3 4

for – Interval operators are used on arrays

 let names = ["Anna", "Alex", "Brian", "Jack"]
for name in names [0...3]
{
    
  print(name)
} // Anna Alex Brian Jack

Unilateral interval ： Let the interval go as far as possible in one direction

for name in names [2...] 
{
    
  print(name)
} // Brian Jack

for name in names [...2] 
{
    
  print(name)
} // Anna Alex Brian

for name in names [..<2]
{
    
  print(name)
} // Anna Alex

let range = ...5
range.contains(7) // false
range.contains(4) // true
range.contains(-3) // true

Interval type

let range1: ClosedRange<Int> = 1...3
let range2: Range<Int> = 1..<3
let range3: PartialRangeThrough<Int> = ...5

character 、 Strings can also use interval operators , But default cannot be used in for-in in

let stringRange1 = "cc"..."ff" // ClosedRange<String>
stringRange1.contains("cb") // false
stringRange1.contains("dz") // true
stringRange1.contains("fg") // false

let stringRange2 = "a"..."f"
stringRange2.contains("d") // true
stringRange2.contains("h") // false

// \0 To ~ It covers all the things that might be needed ASCII character 
let characterRange: ClosedRange<Character> = "\0"..."~"
characterRange.contains("G") // true

Interval values with intervals

let hours = 11
let hourInterval = 2
// tickMark The value of ： from 4 Start , Add up 2, No more than 11
for tickMark in stride(from: 4, through: hours, by: hourInterval) 
{
    
  print(tickMark)
} // 4 6 8 10

switch

var number = 1
switch number {
    
  case 1:
    print("number is 1")
  break
  case 2:
    print("number is 2")
  break
  default:
    print("number is other")
  break
} // number is 1
//case、 default You can't put curly braces after it {}

var number = 1
switch number 
{
    
  case 1:
     print("number is 1")
  case 2:
     print("number is 2")
  default:
     print("number is other")
} // number is 1
// Default can not write break , It doesn't run through the conditions behind it 

fallthrough

Use fallthrough Can achieve penetration effect

var number = 1
switch number 
{
    
  case 1:
     print("number is 1")
     fallthrough
  case 2:
     print("number is 2")
  default:
     print("number is other")
}
// number is 1
// number is 2

switch You have to make sure you can handle all the situations

    
        /* switch Be careful : 1.switch It must be ensured that all situations can be handled  2.case ,default At least one following statement ; 3. If you don't want to do anything , Add one break that will do ; 4. If you can guarantee that all the situations have been handled , You don't have to use default */
        //  If you can guarantee that all the situations have been dealt with , You don't have to use default
enum Answer {
     case right, wrong }
let answer = Answer.right
switch answer 
{
    
  case Answer.right:
       print("right")
  case Answer.wrong:
       print("wrong")
}

Compound condition

switch Also support Character、 String type

let string = "Jack"
switch string
 {
    
  case "Jack":
      fallthrough
  case "Rose":
     print("Right person")
  default:
  break
} // Right person

let character: Character = "a"
switch character 
{
    
  case "a", "A":
      print("The letter A")
 default:
      print("Not the letter A")
} // The letter A

switch string 
{
    
  case "Jack", "Rose":
       print("Right person")
  default:
   break
} // Right person

Interval matching 、 Tuple matching

let count = 62
switch count 
{
    
  case 0:
    print("none")
  case 1..<5:
    print("a few")
  case 5..<12:
    print("several")
  case 12..<100:
    print("dozens of")
  case 100..<1000:
    print("hundreds of")
  default:
    print("many")
} // dozens of

let point = (1, 1)
switch point 
{
    
  case (0, 0):
    print("the origin")
  case (_, 0):
    print("on the x-axis")
  case (0, _):
    print("on the y-axis")
  case (-2...2, -2...2):
    print("inside the box")
  default:
    print("outside of the box")
} // inside the box

// You can use underscores  _  Ignore a value 
// About case Matching problems , Belongs to pattern matching （ Pattern Matching ） The category of 

Value binding

let point = (2, 0)
switch point
 {
    
  case (let x, 0):
    print("on the x-axis with an x value of \(x)")
  case (0, let y):
    print("on the y-axis with a y value of \(y)")
  case let (x, y):
    print("somewhere else at (\(x), \(y))")
} // on the x-axis with an x value of 2
// When necessary, let It can also be changed to var

where

let point = (1, -1)
switch point 
{
    
  case let (x, y) where x == y:
    print("on the line x == y")
  case let (x, y) where x == -y:
    print("on the line x == -y")
  case let (x, y):
    print("(\(x), \(y)) is just some arbitrary point")
} // on the line x == -y

//  Add up all the positive numbers 
var numbers = [10, 20, -10, -20, 30, -30]
var sum = 0
for num in numbers where num > 0 
{
     
  //  Use where To filter num sum += num
}
  print(sum) // 60

Tag statement

outer: for i in 1...4 
{
    
for k in 1...4 
{
    
  if k == 3 
  {
    
    continue outer
  }
  if i == 3
  {
    
   break outer
  }
   print("i == \(i), k == \(k)")
}
}