Java function is not returning expected value

Question

A bug in a program I'm writing as an assignment for my java. Objective: program should take two parameters and find all the odd numbers between those parameters. Then it should return the sum of all those numbers.

Bug: When the parameters are negative or starting number is greater than the ending number, it should return -1. But my program is returning 0.

Maybe my program isn't updating the sum value inside the loop. But even so, as per return condition, my function should return -1, not the sum.

public class SumOddRange{
    public static void main(String[] args){
        System.out.println(sumOdd(10,5));
    }
    
    public static boolean isOdd(int number){
        return (number<0)||(number%2==0)?false:true;
    }
    
    public static int sumOdd(int start, int end){

        int sum = 0;
        for(int i=start; i<=end; i++){
            if(isOdd(i)){
                sum+=i;
            }
        }
        return (start<=0)&&(start>end)? -1: sum;
    }
}

Also, you probably need to do your input check before starting the loop, returning -1 before even getting to the loop if(start < 0 || end < 0 || start > end) return -1; — ernest_k
– ernest_k, Commented Sep 10, 2020 at 10:25
And honestly: you accepted the "wrong" answer. That answer gave you the one line you needed to "fix" your problem. Whereas the other one told so you much more ... — GhostCat
– GhostCat, Commented Sep 10, 2020 at 11:09
Omg. I just thought he is not as experienced as luk2302. So accepting his will give some appreciation or something. — Naveen Kumar
– Naveen Kumar, Commented Sep 10, 2020 at 11:26
I understand that i need to work more on my skills but I'm new to programming and learning. Isn't this all about learning? Thank you so much for suggesting debuggers I just googled what they are. — Naveen Kumar
– Naveen Kumar, Commented Sep 10, 2020 at 11:27

luk2302 · Accepted Answer · 2020-09-10 10:26:41Z

3

Put the input check as the first thing in your method and change the && to an || since you want to return if the first check fails or the second check fails, not only if both fail. And the isOdd can be inlined:

public static int sumOdd(int start, int end){
    if (start <= 0 || start > end)
        return -1;

    int sum = 0;
    for (int i = start; i <= end; i++) {
        if (i % 2 != 0) { // or if (i % 2 == 1) {
            sum += i;
        }
    }
    return sum;
}

answered Sep 10, 2020 at 10:26

luk2302

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Comments

Sadiq Raza · Accepted Answer · 2020-09-10 11:25:56Z

1

There is a logic error in your line return (start<=0)&&(start>end)? -1: sum;

You have to return -1 if start is <0 or start > end, so use "||" (logical Or) instead of "&&" (logical and):

return (start<=0)||(start>end)? -1: sum;

Please go through @luk2302's answer for a better solution.

edited Sep 10, 2020 at 11:25

answered Sep 10, 2020 at 10:33

Sadiq Raza

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4 Comments

GhostCat Over a year ago

Hint: those checks are meant to prevent to loop on invalid numbers. What does it help to check for that AFTER the loop?!

Sadiq Raza Over a year ago

@GhostCat, yes I agree, Ideally he should have checked for invalid inputs first and return -1, if any. Although in this case it gives the right result, it's not efficient.

GhostCat Over a year ago

And honestly, the OP accepted the wrong answer. You just fix his one problem, the other answer does much more than that. But it seems the OP was mainly worried about fixing stuff, not learning something ...

Naveen Kumar Over a year ago

Hey how about you appreciate him for helping. Instead of being toxic.

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