CODEWITHSUNDEEP
javaintsum
Jimmy
Jimmy

Reputation: 847

Better way of calculating sum of even ints

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.");


    }

}

Upvotes: 1

Views: 1631

Answers (4)

A Question Asker
A Question Asker

Reputation: 3311

Why do it with a loop? You can actually calculate it out. Let X be the number they choose. Let N be the largest even number <= X. (N^2+2*N)/4 will be your answer.

Upvotes: 3

whirlwin
whirlwin

Reputation: 16521

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.

Upvotes: 2

Dilum Ranatunga
Dilum Ranatunga

Reputation: 13374

Why use a loop at all? You are computing the sum of:

2 + 4 + ... n, where n is a positive even number.

This is a very simple arithmetic progression.

Upvotes: 2

ninja
ninja

Reputation: 2968

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();

    if (number >= 2) {
        int sumofeven = 0;
        for (int i = 2; i <= number; i += 2) {
            sumofeven += i;
        }
        System.out.println("The sum of the even integers between the number is " + sumofeven);
    } else {
        System.out.println("Invalid number entered.");
    }
}

Upvotes: 0

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