Why are there negative elements in array in this code?

Question

public class Application {
public static void main(String[] args) {

long []a;
a = new long[500];
a[0] = 1;
a[1] = 2;
int sum = 0;

for (int i = 2; i < 500; ++i) {
a[i] = a[i - 1] + a[i - 2];
//System.out.println(a[i]);

if((a[i] == (a[i - 1] + a[i - 2])) && a[i] % 2 == 0) {
System.out.println(a[i]);
sum += a[i];
}

}
sum += 2;

System.out.println("sum : " + sum);

}
}

Answer 1

Here is how the code should look like using the BigInteger class.

import java.math.BigInteger;

public class Application {
public static void main(String[] args) {

BigInteger[] a = new BigInteger [500];
a[0] = new BigInteger("1")
a[1] = new BigInteger("2")

BigInteger sum = new BigInteger("0");

for (int i = 2; i < 500; ++i) {
a[i] = a[i - 1].add(a[i - 2]);

if (a[i].mod(a[1]).equals(new BigInteger("0"))) {
System.out.println(a[i]);
sum = sum.add(a[i]);
}
}
sum = sum.add(a[1]);

System.out.println("sum: " + sum);
}
}

Answer 2

It is because the sum of arrays exceeded the limit of integer, which is 2147483647. For example, if you are trying to add 2147483647 (01111111111111111111111111111111(2)) and 1(00000000000000000000000000000001(2)), the result will be -2147483647(10000000000000000000000000000000(2)), which is negative.

Answer 3

Use BigInteger. It is almost limitless type of integer.

Answer 4

thank you i understand now but if i want to get the sum up to 4 million,what should i do?

Answer 5

thank you very much boris!

Answer 6

https://code.sololearn.com/c6jhrBtgPJ7X/#java
is there any mistake in this code?