package class6_1_Factorial;

import java.util.Scanner;

public class Factorial {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.println("Enter a number to take the factorial of: (Q to quit)");
        while(in.hasNextInt()) {
            int value = in.nextInt();

            System.out.println("factorial(value) = " + factorial(value));
        }
    }

    private static int factorial(int value) {
        if(value < 0) {
            throw new IllegalArgumentException("Cannot take factorial of negative numbers");
        } if(value == 0) {
            return 1;
        } else {
            return value * factorial(value - 1);
        }
    }
}