Question

I’m trying to write a programme to prompt the user to input an int which is above or equal 2. From this input the programme must then calculate and print the sum of all the even integers between 2 and the entered int. It must also produce an error message if the inputted int is below 2. I’ve made a programme for it that works but am just wondering if you guys could find a better way of doing it? I’m sure there is but I can’t quite seem to find a way that works!

Here’s what I did:

import java.util.Scanner;

public class EvenSum {


         public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);

    System.out.println("Enter an integer which is above 2.");
    int number = scan.nextInt();
    int divnum = number / 2;
    int divnum2 = divnum + 1;
    int sumofeven = divnum * divnum2;

    if(number >= 2)
    System.out.println("The sum of the even integers between the number is "+
            sumofeven);
    else
        System.out.println("Invalid number entered.");


    }

}

Answer 1

Note: do not use this example in a real context, it’s not effective. It just shows a more clean way of doing it.

    // Check the input.
    if (number >= 2)
        System.out.println(sum(number));
} 

// Will find the sum if the number is greater than 2.
int sum(int n) {
    return n == 2 ? n - 2 : n % 2 == 0 ? n + sum(n - 2) : sum(n - 1);
}

Hope this helps. Oh, by the way, the method sum adds the numbers recursively.

Sorry, but I had to edit the answer a bit. There might still be room for improvement.