Issue increment sum=0 by long integers pass 9 digits in Java

Question

The program begins by asking the user to give a value assigned to variable n, the user will then be prompted to submit long digits n amounts of times. The digits will then be stored into the initialized array (ar). The function I am trying to create aVeryBigSum is to loop through the numbers in the array, incrementing sum=0 by the numbers in the array to provide the sum (Java).

For some reason however, the program works unless I use two consecutive numbers with greater than 9 digits.

For example:

aVeryBigSum(2,[111111111,111111111]) has n of 2 and two 9 digit numbers in the array

Output:

22222222

aVeryBigSum(2,[1111111111,1111111111]) has n of 2 and two 10 digit numbers in the array Output:

-2072745074

Any idea what the issue might be? I've provided the program below:

import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Main {

    static long aVeryBigSum(int n, long[] ar) {
        int sum  = 0;
        for (int i = 0; i < n; i++){
          System.out.println(sum);
          System.out.println(ar[i]);
          sum += ar[i];
          System.out.println(" ");
        }
        return sum;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        long[] ar = new long[n];
        for(int ar_i = 0; ar_i < n; ar_i++){
            ar[ar_i] = in.nextLong();
        }
        long result = aVeryBigSum(n, ar);
        System.out.println(result);
    }
}

[Scanner is skipping nextLine() after using next(), nextInt() or other nextFoo()?](//stackoverflow.com/q/13102045) or similar. — 001, Dec 29 '17 at 19:04
Possible duplicate of [Why does incrementing a Java int eventually result in a negative number?](https://stackoverflow.com/questions/10968733/why-does-incrementing-a-java-int-eventually-result-in-a-negative-number) — Bernhard Barker, Dec 29 '17 at 20:31
Or one of these two: [Often big numbers become negative](https://stackoverflow.com/q/17218964) / [multiplication of two ints overflowing to result in a negative number](https://stackoverflow.com/q/7215411) — Bernhard Barker, Dec 29 '17 at 20:33

score 1 · Answer 1 · answered Dec 29 '17 at 20:31

1

Your problem is in the line

int sum  = 0;

It should read

long sum = 0;

You are triggering integer overflow when the sum of integers exceeds 32 bits.

answered Dec 29 '17 at 20:31

Mad Physicist

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score 0 · Answer 2 · answered Dec 29 '17 at 22:39

Yes, agree with Mad Physicist. You have to use long sum = 0. But to be the completely correct, you have possibility to have sum greater than Long.MAX_VALUE. You could use e.g. BigDecimal:

static BigDecimal aVeryBigSum(int n, long[] ar) {
    BigDecimal sum = BigDecimal.ZERO;

    for (int i = 0; i < n; i++) {
        System.out.println(sum);
        System.out.println(ar[i]);

        sum = sum.add(new BigDecimal(ar[i]));

        System.out.println(" ");
    }

    return sum;
}

Issue increment sum=0 by long integers pass 9 digits in Java

2 Answers2