Generating Random Numbers

In this lesson you will learn how to generate random numbers with the math/rand package in Go, so you can build things with an element of chance such as dice or rock-paper-scissors. This is for anyone searching for "Go random number generation".

The math/rand package produces random numbers. Use it for dice rolls and raffles. The result changes every time you run it.

The sample code rolls a die from 1 to 6 with rand.Intn(6) + 1 and picks one of Rock, Scissors, and Paper with rand.Intn(len(choices)). Note that the argument of Intn() is exclusive - it means "below this value".

A common stumbling block for beginners is reaching for it in security-sensitive code. Where the values must not be predictable, such as in cryptography, Go's recommended practice is the safer crypto/rand package.

In real-world development random number generation is used widely, from item drops in a game to generating random test data.

📖 Reference code

package main

import (
	"fmt"
	"math/rand"
)

func main() {
	dice := rand.Intn(6) + 1
	fmt.Println("Dice roll:", dice)

	choices := []string{"Rock", "Scissors", "Paper"}
	fmt.Println("Rock-paper-scissors:", choices[rand.Intn(len(choices))])
}

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