go - 以下哪些是 Go 中用于控制循环的有效关键字？

Question

我看到这个问题的正确答案是“for and range”。

但是 for 语句是 Go 中唯一可用的循环语句，并且 range 关键字允许您迭代列表的项目，如数组或映射。为了理解它，您可以将 range 关键字翻译成for each index of。

//for loop
package main

import "fmt"

func main() {
for i := 0; i < 5; i++ {
    fmt.Println("Value of i is now:", i)
    }
}

 //range is used inside a for loop


a := [...]string{"a", "b", "c", "d"}
for i := range a {
    fmt.Println("Array item", i, "is", a[i])
}
capitals := map[string] string {"France":"Paris", "Italy":"Rome",     "Japan":"Tokyo" }
for key := range capitals {
    fmt.Println("Map item: Capital of", key, "is", capitals[key])
    }

//range can also return two items, the index/key and the corresponding value 
for key2, val := range capitals {
    fmt.Println("Map item: Capital of", key2, "is", val)
    }

Answer 1

我认为问题是关于不同形式的 For 循环:
简单的循环变体工作示例:

package main

import "fmt"

func main() {
    //0 1 2 3 4 5 6 7 8 9
    for i := 0; i < 10; i++ {
        fmt.Print(i, " ")
    }
    fmt.Println()

    i := 0
    for ; i < 10; i++ {
        fmt.Print(i, " ")
    }
    fmt.Println()

    for i := 0; i < 10; {
        fmt.Print(i, " ")
        i++
    }
    fmt.Println()

    //2 4 6 8 10 12 14 16 18 20
    for i := 1; ; i++ {
        if i&1 == 1 {
            continue
        }
        if i == 22 {
            break
        }
        fmt.Print(i, " ")
    }
    fmt.Println()

    i = 0
    for {
        fmt.Print(i, " ")
        i++
        if i == 10 {
            break
        }

    }
    fmt.Println()

    for i, j := 0, 0; i < 5 && j < 10; i, j = i+1, j+2 {
        fmt.Println(i, j)
    }
}

对于数组、 slice 、字符串、映射、 channel ，使用 range 关键字:

package main

import "fmt"

func main() {
    ary := [5]int{0, 1, 2, 3, 4}
    for index, value := range ary {
        fmt.Print("ary[", index, "] =", value, " ")
    }
    fmt.Println()
    for index := range ary {
        fmt.Print("ary[", index, "] =", ary[index], " ")
    }
    fmt.Println()
    for _, value := range ary {
        fmt.Print(value, " ")
    }
    fmt.Println()

    slice := []int{20, 21, 22, 23, 24, 25, 26, 27, 28, 29}
    for index, value := range slice {
        fmt.Println("slice[", index, "] =", value)
    }
    fmt.Println()

    str := "Hello"
    for index, value := range str {
        fmt.Println("str[", index, "] =", value)
    }
    fmt.Println()

    mp := map[string]int{"One": 1, "Two": 2, "Three": 3}
    for key, value := range mp {
        fmt.Println("map[", key, "] =", value)
    }
    fmt.Println()

    ch := make(chan int, 10)
    for i := 0; i < 10; i++ {
        ch <- i
    }
    close(ch)

    for i := range ch {
        fmt.Print(i, " ")
    }
    fmt.Println()
}

和标签为 break 标签和 continue 标签:

package main

import "fmt"

func main() {
    a, b := 1, 1
Loop1:
    for {
        b++
    Loop2:
        for {
            a++
            switch {
            case a == 2:
                fallthrough
            case a == 3:
                fmt.Println(3)
            case a == 4, a == 5:
                continue
            case a == 7:
                continue Loop1
            case a == 9:
                break Loop2
            case a == 10:
                break Loop1
            case a == 8:
                break
            default:
                fmt.Println(a, b)
            }
        }
    }
}