# Odd sum application not calculating negative integers correctly?

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4

I'm supposed to create an application that takes a number from the user in order to create a range from 1 to the number that the user enters. I then need to calculate the sum of all odd numbers between 1 and the number that the user enters. This works fine with positive integers but not with negative?

``````import java.util.Scanner;
public class OddSumApplication {
public static void main (String[]args){

int sum = 0;

System.out.print("Enter a positive or negative integer: ");
Scanner in = new Scanner(System.in);
int num = in.nextInt();

if (num == 1){
System.out.println(num);
System.out.println("Sum = " + num);
}
else{
while (num != 1){
if (num >= 1){
if (num % 2 == 1){
sum = sum + num;
num = num - 2;
}
else{
num = num - 1;
}
}
else{
if (num % 2 == 1){
sum = sum + num;
num = num + 2;
}
else{
num = num + 1;
}
}
}
}
sum = sum + 1;
System.out.print("\nSum = " + sum);
}
``````

}

Use the absolute value of `num` and then you do not need `if (num >= 1){...} else {...}` block.

6

It's because negative number % 2 returns negative one. Try to give it into absolute value.

``````...
if (Math.abs(num%2) == 1) {
sum = sum + num;
num = num + 2;
} else {
num = num + 1;
}
``````

posted this

JD