[Illustration] Factorial recursive function [Ruby]

Introduction

When I first learned about recursive functions, I had a hard time understanding them. I understood it by writing it on paper at that time, so I illustrated it this time.

What is a recursive function?

A function that calls itself within the function defined by def ~ end. Fibonacci functions are often treated as an introduction to recursive functions if they are famous. If you are new to this, please search.

What is factorial?

The product of n consecutive natural numbers from> 1 to n is called the factorial of n. Write n !, for example, 4! = 1 × 2 × 3 × 4 = 24. However, the factorial of 0 is 1.

Source: goo dictionary

Code using recursive functions

def factorial(num)
  if num == 1 || num == 0
    return 1
  end
  return num * factorial(num - 1)
end

• If num <0 is passed, it is not considered this time.

It's a very simple code, but it's surprisingly confusing when you think about it in your brain.

Illustrated

At the end

I'm still new to recursive functions, so I'm still confused about complicated things. However, I think that the code illustrated this time is the basis, so if I get lost, I will return to the beginning.

I hope this article helps someone understand recursive functions.