**Introduction**

This article aims to show how you can create a simple function in Julia to get the factorial of a given number.

**What is factorial?**

The product of all integers equal to or less in value than the original number — in other words, a factorial is the number of possible combinations with numbers less than or equal to that number.

We symbolise the factorial of a number with “!” (e.g. 4!).

Some examples

2!=2∙1=2

3!=3∙2∙1=6

4!=4∙3∙2∙1=24

**Logical zero factorial proof**

As we said, a factorial is the number of possible combinations with numbers less than or equal to that number. Zero has no numbers less than it, but it is a number itself. How many arrangements can I do with 0 items? None at all. This is too a way of arrangement, so 0!=1 (none).

Suppose we have three fruits:

🍎🍐🍊

What are the arrangements?

🍎🍐🍊

🍎🍊🍐

🍐🍎🍊

🍐🍊🍎

🍊🍎🍐

🍊🍐🍎

3!=6 as we said previously.

Think similarly for 0!.

**Function in Julia**

```
function f(n::Int64)
f = 1
if n < 0
print("Factorial does not exist for negative numbers")
end
if n == 0
print("The factorial of 0 is 1")
end
if n>0
for i in 1:n
f = f*i
end
println("The factorial is: ",f)
end
end
```

Let’s ask the factorial of -3 (n=-3)

`f(-3)`

Output:

Factorial does not exist for negative numbers

Let’s ask the factorial of 0 (n=0)

`f(0)`

Output:

The factorial of 0 is 1

Let’s ask the factorial of 3 (n=3)

`f(3)`

Output:

The factorial is: 6

Let’s explain the part of the code below:

```
for i in 1:n
f = f*i
end
```

Firstly, we defined the f as 1.

So, we start with f=1.

for i in 1:3

- f=1*1=1
- f=1*2=2
- f=2*3=6 end

That’s simple!

**Conclusion**

In this article, we gave a simple explanation of the factorial as well we made an easy function in Julia!

Thank you for reading!🤗

Article Cover Photo: Photo by Tommy Bond on Unsplash

## Discussion (1)

I liked this article - I wrote a similar one when I was starting out with Julia too!

And then a kind Teacher Assistant for my course came along (with a sneaky smile) and whispered something about some ternary operator...

...Which creeped me out.

Vexed me!

But not as much as when I found out about the world of map, reduce, and folds, and all those nifty iterator methods that can get you out of a pinch: