# Program to generate a random number between L to R

Last Updated : 18 Jan, 2024

Write a program that generates a random number within a specified range [L, R]. The program should take two integers, L and R, as input and output a random number between L and R (inclusive).

Examples:

Input: L = 10, R = 20
Output: 15

Input: L = -5, R = 5
Output: 3

Approach: To solve the problem, follow the below idea:

We can generate a random number in the range [L, R] by finding how many numbers are there between L to R by the formula: diff = (R – L + 1). Now, we can generate a random number and modulo the random number by diff and add the remainder to L to get a random number between L to R.

Step-by-step algorithm:

1. Find the difference between L to R by (R – L + 1).
2. Now, generate a random number and modulo it by the above difference.
3. Scale and shift the random number by adding the remainder to L to fit within the specified range [L, R].

Below is the implementation of the algorithm:

## C++

 #include #include #include   using namespace std;   int main() {     int L = 10, R = 20;       srand(time(NULL));     int random_number = L + rand() % (R - L + 1);       cout << random_number << endl;       return 0; }

## C

 #include #include #include   int main() {     int L = 10, R = 20;       srand(time(NULL));     int random_number = L + rand() % (R - L + 1);       printf("%d\n", random_number);       return 0; }

## Java

 import java.util.Scanner;   public class RandomNumberGenerator {     public static void main(String[] args) {           int L = 10;         int R = 20;           int random_number = L + (int) (Math.random() * (R - L + 1));           System.out.println(random_number);     } }

## Python3

 import random   L, R = 10, 20 random_number = random.randint(L, R)   print(random_number)

## C#

 using System;   class Program {     static void Main()     {         int L = 10;         int R = 20;           Random rand = new Random();         int random_number = rand.Next(L, R + 1);           Console.WriteLine(random_number);     } }

## Javascript

 let L = 10 let R = 20   let random_number = Math.floor(Math.random() * (R - L + 1)) + L;   console.log(random_number);

Output

15

Time Complexity: O(1), as it takes constant time to generate a random number.
Auxiliary Space: O(1)

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