Writing a factorial() function without distinction between 0 and other numbers

Question

This question has been bugging me for quite a while: is it possible to write a factorial function (in any programming language) without any if statement (or similar) which returns 1 when called with 0 as argument too?

Many factorial functions are something like this (Python):

def factorial(n):
    for x in range(1, n):
        n *= x
    return n if n > 0 else 1

But I don't know if it can be done without distinction between varied values of n... What do you think? It is not a matter of speed and optimizing, just my curiosity.

Answer 1

0! is defined as 1.

Here are the results from my code.

0 factorial = 1
1 factorial = 1
2 factorial = 2
3 factorial = 6
10 factorial = 3628800

And here's Java code with no if statement,

package com.ggl.testing;

public class Factorial {

    public static void main(String[] args) {
        int n = 0;
        System.out.println(n + " factorial = " + factorial(n));
        n = 1;
        System.out.println(n + " factorial = " + factorial(n));
        n = 2;
        System.out.println(n + " factorial = " + factorial(n));
        n = 3;
        System.out.println(n + " factorial = " + factorial(n));
        n = 10;
        System.out.println(n + " factorial = " + factorial(n));
    }

    public static long factorial(int n) {
        long product = 1L;

        for (int i = 2; i <= n; i++) {
            product *= (long) i;
        }

        return product;
    }

}