Random numbers

Context

Go provides random number generation in the math/rand package. For cryptographic randomness, use crypto/rand.

Important functions:

• rand.Intn(n) – random integer in [0, n)
• rand.Int() – random non‑negative integer
• rand.Float64() – random float in [0.0, 1.0)
• rand.Seed(seed) – initialize the generator (deprecated in Go 1.20+; now automatic)

Since Go 1.20, the global random generator is seeded automatically at program start.

Example

Generate random numbers.

Code example

package main

import (
    "fmt"
    "math/rand"
    "time"
)

func main() {
    // Random integer between 0 and 99
    fmt.Println("Random int 0-99:", rand.Intn(100))

    // Random float between 0.0 and 1.0
    fmt.Println("Random float:", rand.Float64())

    // Random integer (non-negative)
    fmt.Println("Random int:", rand.Int())

    // For different sequences each run, we can still seed manually (though not required)
    rand.NewSource(time.Now().UnixNano())
    fmt.Println("Seeded random:", rand.Intn(100))
}

Output (example, will vary)

Random int 0-99: 42
Random float: 0.123456789
Random int: 1234567890123456789
Seeded random: 87

Useful links

• math/rand package documentation
• Go by Example: Random Numbers