Program to generate a random three digit even number

Write a program to generate a random three-digit even number.

Examples:

Example 1: 482
Example 2: 736

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

We can generate a random three-digit number by generating a random integer first and then modulo it by 900. Now, after modulo with 900, the remainder can be in the range 0 to 899, so in order to have the remainder as a three-digit number only, we can further add 100 to make the range 100 to 999. If the generated number is equal to 999, then decrement it by 1. Else, if the generated number is an odd number other than 999, increment it by 1 to get the random three-digit even number.

Step-by-step algorithm:

• Generate a random number and modulo it by 900.
• Now, add 100 to the remainder.
• If the generated number is 999, decrement it by 1 to get 998.
• Otherwise, if the generated number is some other three-digit odd number, increment it by 1 to get the required three-digit number.

Below is the implementation of the algorithm:

C++

#include <cstdlib>
#include <ctime>
#include <iostream>

using namespace std;

int main()
{
    srand(time(NULL));
    // Generate a random three-digit number
    int number = (rand() % 900) + 100;
    // Ensure it is even
    if (number == 999) {
        number--;
    }
    else if (number % 2 != 0) {
        number++;
    }
    cout << "Generated number: " << number << endl;
    return 0;
}

C

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main()
{
    srand(time(NULL));
    // Generate a random three-digit number
    int number = (rand() % 900) + 100;
    // Ensure it is even
    if (number == 999) {
        number--;
    }
    else if (number % 2 != 0) {
        number++;
    }
    printf("Generated number: %d\n", number);
    return 0;
}

Java

import java.util.Random;

public class RandomNumberGenerator {
    public static void main(String[] args)
    {
        Random rand = new Random();

        // Generate a random three-digit number
        int number = rand.nextInt(900) + 100;

        // Ensure it is even
        if (number == 999) {
            number--;
        }
        else if (number % 2 != 0) {
            number++;
        }

        System.out.println("Generated number: " + number);
    }
}

Python3

import random


def main():
    # Generate a random three-digit number
    number = random.randint(100, 999)

    # Ensure it is even
    if number == 999:
        number -= 1
    elif number % 2 != 0:
        number += 1

    print("Generated number:", number)


if __name__ == "__main__":
    main()

C#

using System;

class Program {
    static void Main()
    {
        Random rand = new Random();

        // Generate a random three-digit number
        int number = rand.Next(100, 1000);

        // Ensure it is even
        if (number == 999) {
            number--;
        }
        else if (number % 2 != 0) {
            number++;
        }

        Console.WriteLine("Generated number: " + number);
    }
}

Javascript

function generateRandomNumber() {
    // Generate a random three-digit number
    let number = Math.floor(Math.random() * 900) + 100;

    // Ensure it is even
    if (number === 999) {
        number--;
    } else if (number % 2 !== 0) {
        number++;
    }

    return number;
}

// Example usage
const generatedNumber = generateRandomNumber();
console.log("Generated number:", generatedNumber);

Output

Generated number: 448

Time Complexity: O(1), The algorithm generates a random number in constant time.
Auxiliary Space: O(1)