[SOLVED] Generating random numbers over a range in Go

Generating random numbers over a range in Go

All the integer functions in math/rand generate non-negative numbers.

rand.Int() int              // [0, MaxInt]
rand.Int31() int32          // [0, MaxInt32]
rand.Int31n(n int32) int32  // [0, n)
rand.Int63() int64          // [0, MaxInt64]
rand.Int63n(n int64) int64  // [0, n)
rand.Intn(n int) int        // [0, n)

I would like to generate random numbers in the range [-m, n). In other words, I would like to generate a mix of positive and negative numbers.

Solution

For Go 1.22+:

Use the math/rand/v2 package.

import "math/rand/v2"

func randRange(min, max int) int {
    return rand.IntN(max-min) + min
}

For Go 1.21 and earlier:

import "math/rand"

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

Please note that this returns numbers in the range [min, max), meaning that max is never returned. For example, randRange(1, 3) would return 1 and 2 only. It would never return 3. If you want numbers in the range [min, max], just add 1 as shown below:

return rand.IntN(max+1-min) + min