Go by Example: Random Numbers

Go’s math/rand package provides pseudorandom number generation.

 
package main

import "time"
import "fmt"
import "math/rand"

func main() {

For example, rand.Intn returns a random int n, 0 <= n < 100.

 
    fmt.Print(rand.Intn(100), ",")
    fmt.Print(rand.Intn(100))
    fmt.Println()

rand.Float64 returns a float64 f, 0.0 <= f < 1.0.

 
    fmt.Println(rand.Float64())

This can be used to generate random floats in other ranges, for example 5.0 <= f' < 10.0.

 
    fmt.Print((rand.Float64()*5)+5, ",")
    fmt.Print((rand.Float64() * 5) + 5)
    fmt.Println()

The default number generator is deterministic, so it’ll produce the same sequence of numbers each time by default. To produce varying sequences, give it a seed that changes. Note that this is not safe to use for random numbers you intend to be secret, use crypto/rand for those.

 
    s1 := rand.NewSource(time.Now().UnixNano())
    r1 := rand.New(s1)

Call the resulting rand.Rand just like the functions on the rand package.

 
    fmt.Print(r1.Intn(100), ",")
    fmt.Print(r1.Intn(100))
    fmt.Println()

If you seed a source with the same number, it produces the same sequence of random numbers.

 
    s2 := rand.NewSource(42)
    r2 := rand.New(s2)
    fmt.Print(r2.Intn(100), ",")
    fmt.Print(r2.Intn(100))
    fmt.Println()
    s3 := rand.NewSource(42)
    r3 := rand.New(s3)
    fmt.Print(r3.Intn(100), ",")
    fmt.Print(r3.Intn(100))
}

$ go run random-numbers.go
81,87
0.6645600532184904
7.123187485356329,8.434115364335547
0,28
5,87
5,87

See the math/rand package docs for references on other random quantities that Go can provide.

Next example: Number Parsing.

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