Question

I’m stuck on this question from a mock exam paper. I need to multiply a ‘from’ number to a ‘n’ number. In other words: from*(from+1)(from+2)…*n.

I need to solve this problem by using a while loop. I have done this so far and not sure what to do.

class Fact {

    private int factPartND(final int from, final int n) {

        int c = 1;
        int z = from;
        int y = n;
        int num = 0;

        while (y >= z) {

            num += from * (from + c);// need to stop multiplying from for each
                                     // iteration?
            c++;
            y--;
        }

        return num;
    }

    public static void main(String[] args) {
        Fact f = new Fact();
        int test = f.factPartND(5, 11);
        System.out.println(test);
    }

}

Answer 1

Your computation is:

from * (from + 1) * (from + 2) * ... * (from + n)

Think of each factor as one iteration of your loop.

So your second iteration should be multiplying your accumulated value by (from + 1), later another iteration by (from + i), where from < i < n, and so on until you multiply your accumulated value by (from + n).

Your code is very close – you have (from + c) in every iteration, but your arithmetic is wrong.

And as has been mentioned, it’s a bit confusing to use c and y to keep track of your loop, when it’s sufficient to just test c.