如何对从 0 到 1000 的所有整数求和

Question

How to sum all whole numbers to 1000

package proba;

public class Proba {

    public static void main(String[] args) {
        int a = 1;
        int whole = 0;

        int n = 1000;
        int m = 500;
        while (a <= n) {
            if (a % 2 == 0) {
                whole += ;

            }
            a++;
            System.out.println("Rezultat parnih je: " + whole);
        }
    }

}

Answer 1

For all numbers from 0 till 1000, for loop

int sum = 0;
for (int i = 0; i < 1000; i++) {
    sum += i;
}
System.out.println(sum);

For all even numbers, use an if to see if they are even

if (i % 2 == 0) // remainder is 0, meaning even
    sum += i;

Edit: To add even and subtract odd

int sumOfEven;
for (int i = 0; i < 1000; i++) {
    if (i % 2 == 0) {
        sumOfEven += i;
    }
}

int sumOfOdd;
for (int i = 0; i < 500; i++) {
    if (i % 2 != 0) {
        sumOfOdd += i;
    }
}
System.out.println(sumOfEven - sumOfOdd); // Math.absolute can also be done here for a non-negative value

Answer 2

Adding all numbers just to subtract later 250 of them is not efficient. Just filter the ones you don't want in the total sum

int sum = IntStream.rangeClosed(1, 1000)
                   .filter(i -> i >= 500 || i % 2 == 0)
                   .sum();
System.out.println(sum);