Random in Kotlin

I think you have come across the concept of "coincidence" many times. It didn't matter whether it was a lottery or something else. Our life is constantly beset by one or another accident. Let's take a look at how random works in Kotlin.

Random

When talking about randomness in Kotlin, any Kotlin developer will immediately think of kotlin.random package that is built into Kotlin.

With its help you can:

generate random numbers: integers (Int, Long) and floating point (Float, Double)
generate a random logical type Boolean

It doesn't hurt to know

Also, kotlin.random can generate bytes and bits, but we haven't covered those types yet.

Let's move on to the more practical part. How is it all done?

To get a random integer, we can use Random.nextInt(from, until) function:

Main.kt
import kotlin.random.Random

fun main() {
    println(Random.nextInt(0, 9))
}

Outputs:

Console

That is, randomness is limited from 0 to 9.

Attention

There can be any numbers, the main thing is not to mix their 'from' with 'to' and not do the next Random.nextInt(9, 0). There will be an error!

Other functions work similarly:

Main.kt
import kotlin.random.Random

fun main() {
    println(Random.nextInt(0, 9))
    println(Random.nextLong(1L, 1000000L))
    println(Random.nextDouble(1.9, 9.9))
    println(Random.nextBoolean())
}

It will output something like this:

Console
2
386039
7.176104912683028
false

Let's solve the following task:

Task #1

The user enters a number from 1 to 30 (check the number). Make a program that will guess the user's number and print how many tries it took to guess the given number.

First, let's get a number and check it:

fun main() {
    val number = readln().toInt()
    if (number < 0 || number > 30) {
        println("The number must be between 1 and 30.")
        return // exit the function
    }
}

Now, in order to guess the number, we can use the while loop operator

import kotlin.random.Random // add the Random type to our namespace

fun main() {
    val number = readln().toInt()
    if (number < 0 || number > 30) {
        println("The number must be between 1 and 30.")
        return // exit the function
    }

    var attempt = 0 // make a variable to store the number of attempts
    while (true) {
        if (Random.nextInt(0, 30) == number) {
            println("The number was found for $attempt") // we do concatenation
            break // exit the loop
        }
        attempt++ // add 1 to attempt
    }
}

Interesting to know

Some obscure attempt++, right? It's actually just a simplification for attempt = attempt + 1. It also exists in the other direction: attempt--.

By the way, this operation has two types:

prefix increment / decrement
postfix increment / decrement

In our case, this is a postfix increment. But how are they different?

The prefix increment first adds and then returns the value from the expression, while the postfix increment increment first returns a value and then adds one. That is:

var x = 0
println(x++) // will output 0
println(x) // only here it will output 1

var y = 0
println(++y) // will print 1

And we solved this simple problem.

Random in Kotlin

Random​

Random