分支语句

单分支语句

  1. func main() {
  2.     s := "屌丝"
  4.     if s == "屌丝" {
  5.         fmt.Println("左手一个，右手一个")
  6.     }
  8.     // if支持1个初始化语句，初始化语句和判断条件以分号分隔
  9.     if a := 10; a == 10 {
  10.         fmt.Println("a = 10")
  11.     }
  13.     a := 8
  14.     if a == 10 {
  15.         fmt.Println("a==10")
  16.     } else if a > 10 {
  17.         fmt.Println("a>10")
  18.     } else if a < 10 {
  19.         fmt.Println("a<10")
  20.     } else {
  21.         fmt.Println("这是不可能的！！")
  22.     }
  23. }

多分支语句

switch

  1. func main() {
  2.     num := 12
  3.     switch num {
  4.     case 1:
  5.         fmt.Println("按下的是1楼")
  6.         // break //go保留了break关键字，跳出语句；默认就是break
  7.         fallthrough        //继续无条件执行下一个条件语句
  8.     case 2:
  9.         fmt.Println("按下的2楼")
  10.         // break
  11.     case 3:        // case后面支持多个条件
  12.         fmt.Println("按下的3楼")
  13.         // break
  14.     case 4:
  15.         fmt.Println("按下的4楼")
  16.         // break
  17.     default:
  18.         fmt.Println("按下的xxxx楼")
  19.     }
  22.     socre := 85
  23.     switch {
  24.     case socre > 90:
  25.         fmt.Println("优秀")
  26.     case socre > 80:
  27.         fmt.Println("良好")
  28.     case socre > 70:
  29.         fmt.Println("一般")
  30.     default:
  31.         fmt.Println("other....")
  32.     }
  35. }

循环语句

for

  1. func main() {
  2.     sum := 0
  4.     for i := 1; i <= 100; i++ {
  5.         sum += i
  6.     }
  7.     fmt.Println("sum = ", sum)
  8. }

break

  • 跳出循环
  • 跳出到指定 tag
  1. package main
  3. import "fmt"
  5. func main() {
  7.     outer:
  9.     for i:=0; i< 10; i++ {
  10.         for j := 0; j<10; j ++ {
  11.             if i == 5 {
  12.                 break outer
  13.             }
  15.             fmt.Printf("i, j = %d, %d\t", i, j )
  16.         }
  18.         fmt.Println()
  19.     }
  21.     fmt.Println("main outer....")
  22. }

输出

  1. D:\projects\gocode\go100\breakdemo
  2. λ go run main.go
  3. i, j = 0, 0     i, j = 0, 1     i, j = 0, 2     i, j = 0, 3     i, j = 0, 4     i, j = 0, 5     i, j = 0, 6     i, j = 0, 7     i, j = 0, 8     i, j = 0, 9
  4. i, j = 1, 0     i, j = 1, 1     i, j = 1, 2     i, j = 1, 3     i, j = 1, 4     i, j = 1, 5     i, j = 1, 6     i, j = 1, 7     i, j = 1, 8     i, j = 1, 9
  5. i, j = 2, 0     i, j = 2, 1     i, j = 2, 2     i, j = 2, 3     i, j = 2, 4     i, j = 2, 5     i, j = 2, 6     i, j = 2, 7     i, j = 2, 8     i, j = 2, 9
  6. i, j = 3, 0     i, j = 3, 1     i, j = 3, 2     i, j = 3, 3     i, j = 3, 4     i, j = 3, 5     i, j = 3, 6     i, j = 3, 7     i, j = 3, 8     i, j = 3, 9
  7. i, j = 4, 0     i, j = 4, 1     i, j = 4, 2     i, j = 4, 3     i, j = 4, 4     i, j = 4, 5     i, j = 4, 6     i, j = 4, 7     i, j = 4, 8     i, j = 4, 9
  8. main outer....

迭代语句

range

  1. func main() {
  2.     str := "hello"
  4.     // 传统方式 for
  5.     // for i := 0; i < len(str); i++ {
  6.     //     fmt.Printf("str[%d] = %c\n", i, str[i])
  7.     // }
  9.     // for + range 迭代， 类似 python enumerate
  10.     for idx, data := range str {
  11.         fmt.Printf("str[%d] is %c\n", idx, data)
  12.     }
  14.     for idx, _ := range str {    // 支持匿名变量
  15.         fmt.Printf("str[%d] is %c\n", idx, str[idx])
  16.     }
  18. }

练习： 打印99乘法表

  1. func main() {
  2.     for i := 1; i <= 9; i++ {
  3.         for j := 1; j <= i; j++ {
  4.             fmt.Printf("%d * %d = %d    ", j, i, j*i)
  5.         }
  6.         fmt.Println("")
  7.     }
  8. }
  9. /*
  10. 1 * 1 = 1
  11. 1 * 2 = 2    2 * 2 = 4
  12. 1 * 3 = 3    2 * 3 = 6    3 * 3 = 9
  13. 1 * 4 = 4    2 * 4 = 8    3 * 4 = 12    4 * 4 = 16
  14. 1 * 5 = 5    2 * 5 = 10    3 * 5 = 15    4 * 5 = 20    5 * 5 = 25
  15. 1 * 6 = 6    2 * 6 = 12    3 * 6 = 18    4 * 6 = 24    5 * 6 = 30    6 * 6 = 36
  16. 1 * 7 = 7    2 * 7 = 14    3 * 7 = 21    4 * 7 = 28    5 * 7 = 35    6 * 7 = 42    7 * 7 = 49
  17. 1 * 8 = 8    2 * 8 = 16    3 * 8 = 24    4 * 8 = 32    5 * 8 = 40    6 * 8 = 48    7 * 8 = 56    8 * 8 = 64
  18. 1 * 9 = 9    2 * 9 = 18    3 * 9 = 27    4 * 9 = 36    5 * 9 = 45    6 * 9 = 54    7 * 9 = 63    8 * 9 = 72    9 * 9 = 81
  19. */

range 变量地址

  1. package main
  3. import (
  4.     "fmt"
  5.     "os"
  6. )
  8. func main() {
  9.     var s, sep string
  11.     for _, arg := range os.Args[1:] {
  12.         fmt.Printf("arg addr: %v, value: %v\n", &arg, arg)
  13.         s += sep + arg
  14.         sep = " "
  15.     }
  17.     fmt.Println(s)
  19. }

输出

  1. D:\projects\gocode\studylib\gopro01>go run main.go 11 aa bb
  2. arg addr: 0xc0000881e0, value: 11
  3. arg addr: 0xc0000881e0, value: aa
  4. arg addr: 0xc0000881e0, value: bb
  5. 11 aa bb

跳出/过循环

  • break 跳出本层循环；可用于fro, switch, select
  • continue 跳过本次循环，继续下一次循环；只能用于for

goto语句

goto可以用在任何地方，但是不能跨函数使用

  1. func main() {
  2.     fmt.Println("11111111111")
  3.     goto End
  4.     fmt.Println("2222222222222")
  5. End:
  6.     fmt.Println("end end end end end")
  7. }