Go基础 - 3 条件语句

判断语句if

package main

import "fmt"

func main() {

    if number := 7; number < 1 {
        fmt.Println(1)
    } else if number >= 1 && number <= 10 {
        fmt.Println(2)
    } else {
        fmt.Println(3)
    }

}

2

选择语句switch

package main

import "fmt"

func main() {

    switch number1 := 3; number1 {
    case 1:
        fmt.Println(1)
    case 3:
        fmt.Println(3)
    case 5:
        fmt.Println(5)
    }
    //不需要写break，一旦条件符合自动结束

    number2 := 6
    switch {
    case number2 == 2:
        fmt.Println(2)
    case number2 == 4:
        fmt.Println(4)
    case number2 == 6:
        fmt.Println(6)
        //如希望继续执行下一个case，可以使用fallthrough语句
        fallthrough
    default:
        fmt.Println("default")
    }

}

3
6
default

循环语句 for

package main

import "fmt"

func main() {
    //形式一:
    for number1 := 1; number1 < 3; number1++ {

        fmt.Printf("number1:%d\n", number1)
    }
    //形式二:
    number2 := 1

    for number2 < 3 {

        fmt.Printf("number2:%d\n", number2)
        number2++ //不能写成 number2 = number2++(++ 与 -- 是作为语句而不是作为表达式)
    }
    //形式三: for没有条件将无限循环;用break 退出循环
    for {

        fmt.Println("loop")
        break
    }

}

number1:1
number1:2
number2:1
number2:2
loop

遍历 range

package main

import "fmt"

func main() {
    // range 关键字用于for循环中迭代数组(array)、切片(slice)、通道(channel)或集合(map)的元素
    number := [5]string{"a", "b", "c", "d", "e"}

    for k, v := range number {
        fmt.Println(k, v)
    }

    /* 省略key的写法
        for _, v := range number {
            fmt.Println(v)
        }
    */

}

0 a
1 b
2 c
3 d
4 e

跳转语句goto, break, continue

• 支持函数内部 goto 跳转, continue 进入一下次循环，break 终止循环
• break 和 continue 都可以配合标签,在多级嵌套循环间跳出.这和 goto 调整执行位置完全不同
• 通常建议往后 goto,避免死循环

package main

import "fmt"

func main() {

    for number := 1; number < 5; number++ {
        if number == 3 {
            break
        }
        fmt.Println("break:", number)
    }

    for number := 1; number < 5; number++ {
        if number == 3 {
            continue
        }
        fmt.Println("continue:", number)
    }
lable1:

    for {
        for {
            //配合标签跳出最外层循环
            //标签名是大小写敏感的
            break lable1
        }
    }

    fmt.Println("Hello World1")

    goto lable2

    fmt.Println("Hello World2")

lable2:
    fmt.Println("Hello World3")

}

break: 1
break: 2
continue: 1
continue: 2
continue: 4
Hello World1
Hello World3