如何从范围中选择一个随机数？

Question

I read the documentation for the function Intn https://golang.org/pkg/math/rand/#Intn but I don't understand what they mean I know how random differs from pseudo-random. But how can I simulate a random in the range from 1 to 1000 for example?

package main
import (
    "fmt"
    "math/rand"
)

func main() {
    fmt.Println(randInt(1, 1000))
}

func randInt(min int, max int) int {
    return min + rand.Intn(max-min)
}

The answer is always 879

func main() {
    fmt.Print(rand.Intn(100))
}

The answer is always 81

Answer 1

You need to "Seed" the random number generator. This is like the code that tells the pseudo random number generator how to generate your numbers. Now, you can't just give this any number, or you are going to generate the same set every time. Often a good practice is to seed with the current time.

package main
import (
    "fmt"
    "math/rand"
    "time"    #ADDED
)

func main() {
    // Seed should be set once, better spot is func init()
    rand.Seed(time.Now().UTC().UnixNano())   #ADDED
    fmt.Println(randInt(1, 1000))
}

func randInt(min int, max int) int {
    return min + rand.Intn(max-min)
}

Now every time you call your randInt() function, it will use the time from when the seed function was called to generate the random number.