Binary Addition using Java

Question

I have to sum binary numbers, I'm using reverse loop like we actually sum using pen & paper. So there is this hard-coded array of two integers whose length I have made equal in order to avoid any discrepancy. I'm checking whether sum & carry value matches then output should be made so & so otherwise so & so. Check code below.

My question is why am I getting error on running as to Array Index Out of Bounds -1, even after a successful compilation.

public class binary{

static int sum, carry;
static int output = 0;


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

        for(int i = 10; i >= 0; i--)
        {
            if(a[i] == 0 && b[i] == 0)
            {
                sum = 0;
                carry = 0;

            }
            if(a[i] == 0 && b[i] == 1)
            {
                sum = 1;
                carry = 0;

            }
            if(a[i] == 1 && b[i] == 0)
            {
                sum = 1;
                carry = 0;

            }
            if(a[i] == 1 && b[i] == 1)
            {
                sum = 0;
                carry = 1;

            }
            if(carry == 1)
            {
                carry += a[i-1] + b[i-1];
                output = carry;
            }
            else
            {
                output += a[i] + b[i];
                output = sum;
            }
            System.out.print(output); 
        } 
    }
}

In your `if(carry ==1)` you have `i-1`. When `i=0` this will be att index `-1` -> out of bounds — Aidin, Dec 22 '16 at 14:12
How do you see the two codes similar. That's an ordered loop. And I'm using reverse loop. — Swati Sharma, Dec 22 '16 at 14:12
the codes are not similar but using the answer on the linked question, you will find how to solve your problem — ᴄʀᴏᴢᴇᴛ, Dec 22 '16 at 14:14
The issue is not the type of code, but the problem is the same. Out of bounds is Out of bounds no matter the code, the solution will also be the same - keep within the bounds — Aidin, Dec 22 '16 at 14:15
"even after a successful compilation." `ArrayIndexOutOfBoundsException` is a runtime error; it has nothing to do with successful compilation. — Andy Turner, Dec 22 '16 at 14:22

score 0 · Answer 1 · answered Dec 22 '16 at 14:12

 if(carry == 1)
    {
        carry += a[i-1] + b[i-1];
        output = carry;
    }

This is the part that is causing the array out of bound exception..since for i=0 the carry will contain a[-1]+b[-1] which are of course out of bound(0 and 10 being the bounds)

score 0 · Accepted Answer · edited Dec 22 '16 at 14:24

0

carry += a[i-1] + b[i-1];

If i is 0 then you will get index -1.

edited Dec 22 '16 at 14:24

Aidin

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answered Dec 22 '16 at 14:12

fg78nc

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Thanks I will add break and try to solve further.. – Swati Sharma Dec 22 '16 at 14:36

Binary Addition using Java

2 Answers2