Question

I am currently taking pre-calculus and thought that I would make a quick program that would give me the results of factorial 10. While testing it I noticed that I was getting incorrect results after the 5th iteration. However, the first 4 iterations are correct.

public class Factorial
{
    public static void main(String[] args)
    {

        int x = 1;
        int factorial;

        for(int n = 10; n!=1; n--)
        {

            factorial = n*(n-1);
            x = x * factorial;
            System.out.printf("%d ", x);

        }

    }//end of class main
}//end of class factorial

Answer 1

You’re surpassing the capacity of the int type (2,147,483,647), so your result is wrapping back around to the minimum int value. Try using long instead.

Having said the that, the method you are currently employing will not result in the correct answer: actually, you are currently computing 10! ^ 2.

Why complicate things? You could easily do something like this:

long x = 1L;

for(int n = 1; n < 10; n++)
{
    x *= n;
    System.out.println(x);
}

1
2
6
24
120
720
5040
40320
362880

which shows successive factorials until 10! is reached.

Also, as others have mentioned, if you need values bigger than what long can support you should use BigInteger, which supports arbitrary precision.