Write a factorial method which takes as its input a non-negative integer and calculates the factorial of that number. The factorial of a number is the product of all integers from 1 up to that number. For example: factorial(5) == 5 * 4 * 3 * 2 * 1 == 120 The factorial of 0 is defined to be 1. See the Wikipedia article on the factorial for more i…

Implement the factorial function

def factorial(n)
  result = 1 # you need somewhere to store the result, and since this is multiplication, you can't start at 0. 
                 #THIS HAS TO BE OUTSIDE THE LOOP. Otherwise everytime it goes to the next i element result will go back to being 1.
  n.downto(1) do |i|
    result = result * i # here result and i are multiplied first, then the result is assigned to the result variable. Let me know if this is confusing. 
  end
  # now, we've looped through all of the numbers and multiplied them, but the loop does not return anything.
  return result # this will return the result that we ended up with after looping or iterating through.
end

# or

def factorial(n)
  result = 1
  n.downto(1) do |i|
    result *= i # this is shorthand for result = result * i
  end
  result #we don't need the return, ruby automatically returns the value that is the last part of a method
end