https://jackxiang.com/index.php zh-cn https://jackxiang.com/post// jack <xdy108@126.com> Sun, 06 Mar 2022 14:36:51 +0000 https://jackxiang.com/post// package main import(         "fmt"         "math/rand"         "time" ) func main(){         rand.Seed(time.Now().Unix())         if num := rand.Intn(3); num == 0 {                 fmt.Println(num)                 fmt.Println("Space Adventures")         } else if num == 1 {                 fmt.Println(num)                 fmt.Println("SpaceX")         }else{                 fmt.Println(num)                 fmt.Println("Virgin Galactic")         } }

go build short-if.go  
./short-if
1
SpaceX

./short-if
2
Virgin Galactic

./short-if
0
Space Adventures


如果不加：
        rand.Seed(time.Now().Unix())

其值一直是：2

原因是：https://blog.csdn.net/weixin_33816821/article/details/94581126


Go语言的switch语法学习之num的简短声明也可用于switch语句的一部分：
package main import(         "fmt"         "math/rand"         "time" ) func main(){         rand.Seed(time.Now().Unix())         switch num := rand.Intn(10); num {         case 0:                 fmt.Println("Space Adventure")         case 1:                 fmt.Println("SpaceX")         case 2:                 fmt.Println("Virgin Galactic")         default:                 fmt.Println("Random spaceline #",num)         } }

./short-switch
Virgin Galactic

./short-switch  
Random spaceline # 4


cat scope-rules.go   #几月有多少天的一个判断：
package main import(         "fmt"         "math/rand"         "time" ) var era = "AD" func main(){         year := 2018         rand.Seed(time.Now().Unix())         switch month := rand.Intn(12) + 1;month {         case 2:             day  := rand.Intn(28) + 1             fmt.Println(era, year, month, day)         case 4, 6, 9, 11:             day := rand.Intn(30) + 1             fmt.Println(era, year, month, day)         default:             day := rand.Intn(31) + 1             fmt.Println(era, year, month, day)         } }


./scope-rules
AD 2018 10 24


        default:
            day := rand.Intn(31) + 1
            fmt.Println(era, year, month, day)
        }
        fmt.Println(month,day)  //作用域不再有了。
go build scope-rules.go      
# command-line-arguments
./scope-rules.go:22:14: undefined: month
./scope-rules.go:22:20: undefined: day


包括switch的每个case也是都拥有自己独立的作用域，每个分支里面的day变量在分支结束后，day变量将不再处于作用域之内，switch分支的作用域是唯一一种无需使用大括号标识的作用域。


cat random-date.go
package main import(         "fmt"         "math/rand"         "time" ) var era = "AD" func main(){         rand.Seed(time.Now().Unix())         year := 2018         month := rand.Intn(12) + 1         daysInMonth := 31         switch month {         case 2:             daysInMonth = 28         case 4, 6, 9, 11:             daysInMonth = 30         }         day := rand.Intn(daysInMonth) + 1         fmt.Println(era, year, month, day) }


#./random-date
AD 2018 11 30

#./random-date
AD 2018 11 30


研究下闰年：
cat random-date-study.go
package main import(         "fmt"         "math/rand"         "time" ) var era = "AD" func main(){         rand.Seed(time.Now().Unix())         year := 2018 + rand.Intn(5)         //year := 2000         leep := year%400 == 0 || (year%4 == 0 && year%100 != 0)  //是否是闰年Boole         month := rand.Intn(12) + 1         daysInMonth := 31         switch month {         case 2:             if leep{                daysInMonth = 29             } else {                daysInMonth = 28             }         case 4, 6, 9, 11:             daysInMonth = 30         }         for i := 0;i < 10 ;i++ {           day := rand.Intn(daysInMonth) + 1           fmt.Println(era, year, month, day)         } }

./random-date-study
AD 2000 2 18
AD 2000 2 4
AD 2000 2 6
AD 2000 2 8
AD 2000 2 7
AD 2000 2 21
AD 2000 2 7
AD 2000 2 29
AD 2000 2 12
AD 2000 2 12 ]]> https://jackxiang.com/post//#blogcomment <user@domain.com> Thu, 01 Jan 1970 00:00:00 +0000 https://jackxiang.com/post//#blogcomment