Swift 2 学习笔记 3.逻辑控制

课程来自慕课网liuyubobobo老师

逻辑控制

• 循环结构
  • for in 循环

  for i in 1..<10{
      print(i)  // 1~9
  }
  
  var resule = 1
  var base = 2
  for _ in 1...10{
      resule *= base
  }
  resule  // 1024
  

  • while 循环

  // a b扔骰子，谁先连赢三局
  var aWin = 0
  var bWin = 0
  var game = 0
  
  while aWin < 3 && bWin < 3 {
      game += 1
  
      let a = arc4random_uniform(6) + 1
      let b = arc4random_uniform(6) + 1
  
      if a > b {
          print("a Win")
          aWin += 1
          bWin = 0
      }else if b > a {
          print("b Win")
          bWin += 1
          aWin = 0
      }else{
          print("Draw")
          aWin = 0
          bWin = 0
      }
  }
  
  let winner = aWin == 3 ? "a" : "b"
  print("Winner is \(winner)")
  

  • repeat while 循环

  // a b扔骰子，谁先连赢三局
  var aWin = 0
  var bWin = 0
  var game = 0
  
  repeat{
      game += 1
  
      let a = arc4random_uniform(6) + 1
      let b = arc4random_uniform(6) + 1
  
      if a > b {
          print("a Win")
          aWin += 1
          bWin = 0
      }else if b > a {
          print("b Win")
          bWin += 1
          aWin = 0
      }else{
          print("Draw")
          aWin = 0
          bWin = 0
      }
  }while aWin < 3 && bWin < 3
  
  let winner = aWin == 3 ? "a" : "b"
  print("Winner is \(winner)")
  

  • 循环控制

  // a和b掷骰子直到分出胜负
  while true {
      let a = arc4random_uniform(6)+1
      let b = arc4random_uniform(6)+1
  
      if a == b {
          print("draw")
          continue  // 平局 再比一次
      }
  
      let winner = a > b ? "a" : "b"
      print("winner is \(winner)")
      break  // 分出胜负 跳出循环
  }
  

• 选择结构
  • if 结构

  let passWord = "jilei"
  if passWord == "jilei" {
      print("Pass")
  }else{
      print("Error")
  }
  

  • switch 结构

  // switch 语句必须穷举全部可能性
  let rating = "A"
  switch rating{
  case "A":
      print("Great!")
  case "B":
      print("Just so so.")
  case "C":
      print("It's bad!")
  default:
      break
  }
  

  • switch 的更多用法

  case "A","a":  // 多个匹配值
  case 1..<60:  // 范围匹配值
  // 元组
  case (0,0):  
  case (_,0):  // 忽略元组中第一个值
  case (let x,0):  // 忽略元组中第一个值，之后需要使用
  case (-1...1,-1...1):
  
  // fallthrough 允许跳入下一个case
  let x = (0,0)
  
  switch x {
  case (0,0):
      print("It's origin!")
      fallthrough
  case (_,0):
      print("It's on the x-axis.")
      fallthrough
  case (0,_):
      print("It's on the y-axis.")
  default:
      print("It's just an ordinary point")
  }
  // It's origin!"
  // It's on the x-axis.
  // It's on the y-axis.
  

  • 控制转移

  // x^4 - y^2 = 15xy 求一个300内的整数解
  findAnswer:
  for x in 1...300 {
      for y in 1...300 {
          if x*x*x*x - y*y == 15*x*y {
              print(x,y)
              break findAnswer  //跳出findAnswer循环
          }
      }
  }
  // 4 4
  

  • where 与 模式匹配

  // 点在 x=y 直线上
  case let (x,y) where x == y:
  
  // Swift3 使用 , 代替 where 进行约束
  let age = 19
  if case 10...19 = age, age >= 18 {
      print(age)
  }
  
  //1到100之内能被3整除的整数
  for case let i in 1...100 where i%3==0 {
      print(i)
  }
  

  • guard 与 代码风格初探

  func buy(money: Int, price: Int, capacity: Int, volume: Int){
      guard money >= price else{
          print("Not enough money")
          return
      }
      guard capacity >= volume else{
          print("Not enough capacity")
          return
      }
      print("Buy it!")
  }