Having trouble writing a method that factors negative numbers.

[Angela Li]

I am trying to write a method that returns the list of factors when I input an integer.

private ArrayList<Integer> getIntegerFactors(int n) {
		ArrayList<Integer> factor = new ArrayList<Integer>();
		if(n>0){
			for (int i = 1; i <= n; i++) {
				if (n % i == 0) {
					factor.add(n / i);
					int m = -i;
					factor.add(n/m);
				}
			}
			return factor;
		}
			else if(n<0){
			for (int i = 1; i >= n; i--) {
				if (n % i == 0) {
					factor.add(n / i);
					int m = -i;
					factor.add(n/m);
					}
				}
			}
			return factor;
		}
	}

When I run it using my main I get an error message:
Exception in thread "main" java.lang.ArithmeticException: / by zero
at QuadraticEqn.getIntegerFactors(QuadraticEqn.java:51)
at QuadraticEqn.main(QuadraticEqn.java:9)

What am I doing wrong?

[Persio Berberian]

Are you inputing a negative number?

[Rob Spoor]

Angela Li wrote:

			else if(n<0){
			for (int i = 1; i >= n; i--) {

i starts at 1, then becomes 0. That will cause n % i to fail. Make i start at -1 instead.

[Campbell Ritchie]

Set a boolean negative flag, take the absolute value of the number, factorise it, and if (negative) add -1 to the list of factors.

[Angela Li]

Thanks Rob, I didn't realize that.

[Rob Spoor]

You're welcome. But Campbell does have a point - my code will miss one or two factors. His approach is much better.