How to generate random numbers in a given range in Go

Overview

Go provides a built-in package named math/rand to generate pseudorandom numbers.

The pseudorandom numbers are a deterministic sequence of numbers that depend on a seed value. In order to generate random numbers on every execution, we need to set the seed every time.

Note: You can learn more about seed here.

In this shot, we’ll see how to generate a random number in a given range using the rand.Intn() function of the math/rand package.

rand.Intn() function

rand.Intn(n)

The rand.Intn() function accepts a number n and returns an unsigned pseudorandom integer in the interval [0, n). It will throw an error if the value of n is less than zero.

Generate random number in a specific range

We can use the following syntax to generate a random number in a specific range.

rand.Intn(max-min) + min

Here, max is the upper bound and min is the lower bound. It will return a random number in the interval [min, max).

Code

Let’s see an example to generate a random number between 1 and 5.

Packages

We will use the following packages.

  • fmt formats the output.
  • math/rand generates random numbers.
  • time sets the seed.
package main
import (
  "fmt"
  "math/rand"
  "time"
)
func main() {
  min := 1
  max := 5
  // set seed
  rand.Seed(time.Now().UnixNano())
  // generate random number and print on console
  fmt.Println(rand.Intn(max - min) + min)
}

Explanation

  • Lines 3–7: We import all the necessary packages.
  • Lines 10–11: We declare 2 variables min and max that specify the lower and the upper bound respectively.
  • Line 13: We set a seed using time.Now().UnixNano() function. This function will return the number of seconds passed from January 1, 1970.
  • Line 15: We generate the random number using the rand.Intn() function and output it on the console.

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