流程控制

If/Else 分支

package main

import "fmt"

func main() {
  young(20)
  isUsingNewVariable(100, 200)
}

func young(age int) {
  if age < 18 {
    println("I am a child")
  } else if age > 18 && age < 30 {
    println("I am young")
  } else {
    println("I am old")
  }
}

func isUsingNewVariable(start int, end int) {
  if distance := end - start; distance > 100 {
    fmt.Printf("Too far away :%d\n", distance)
  } else {
    fmt.Printf("short away: %d\n", distance)
  }

  // 这里不能访问  distance
  //fmt.Printf("distance: %d\n", distance)
}

For 循环

package main

import "fmt"

func main() {

    i := 1
    for i <= 3 {
        fmt.Println(i)  // 1 2 3
        i = i + 1
    }

    for j := 7; j <= 9; j++ {
        fmt.Println(j)  // 7 8 9
    }

    for {
        fmt.Println("loop")  // loop
        break  // 跳出循环
    }

    for n := 0; n <= 5; n++ {
        if n%2 == 0 {
            continue  // 直接进入下一次循环
        }
        fmt.Println(n)  // 1 3 5
    }
}

func forI() {
  arr := []int{10, 20, 30, 40, 50}
  for i := 0; i < len(arr); i++ {
    fmt.Printf("index: %d, value: %d\n", i, arr[i])
  }
}

func forR() {
  arr := []int{1, 2, 3, 4, 5}
  for index, value := range arr {
    fmt.Printf("index: %d, value: %d\n", index, value)
  }

  // 只需要value
  for _, v := range arr {
    fmt.Printf("value: %d\n", v)
  }

  // 只需要index，建议用fori
  for index := range arr {
    fmt.Printf("index: %d\n", index)
  }
}

Switch 分支结构

package main

import (
  "fmt"
  "time"
)

func main() {
  i := 2
  fmt.Print("write ", i, " as ")
  switch i {
  case 1:
    fmt.Println("one")
  case 2:
    fmt.Println("two")  // Write 2 as two
  case 3:
    fmt.Println("three")
  default:
    fmt.Println("other")
  }

  t := time.Now()
  switch {
  case t.Hour() < 12:
    fmt.Println("It's before noon")
  default:
    fmt.Println("It's after noon")
  }
}

Select

package main

import (
  "time"
)

func main() {
  ch1 := make(chan string)
  ch2 := make(chan string)

  go func() {
    time.Sleep(time.Second * 2)
    ch1 <- "message from channel1"
  }()

  go func() {
    time.Sleep(time.Second)
    ch2 <- "message from channel2"
  }()

  // select 同时的情况下，顺序是随机的
  for i := 0; i < 2; i++ {
    select {
    case msg := <-ch1:
      println(msg)
    case msg := <-ch2:
      println(msg)
    case <-time.After(time.Second * 2):
        println("timeout")
    }
  }
}