Go by Example: Random Numbers

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

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

Depending on where you run this sample, some of the generated numbers may be different. Note that on the Go playground seeding with time.Now() still produces deterministic results due to the way the playground is implemented.

 
$ 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.

by Mark McGranaghan and Eli Bendersky | source | license