"""
 factorial.py
 
   factorial(n) = n*(n-1)*(n-2)* ... * 3*2*1
 
   factorial(6) = 6*5*4*3*2*1 = 

   8! = 8 * 7 * 6 * 5 * 4 * 3 * 2 1
   8! = 8 * 7!

   factorial(n) = n * factorial(n-1)


In class May 13
 
"""

def fact_loop(n):
    """ Calcuate the factorial of n using a loop """
    answer = 1
    while n > 1:
        answer = answer * n
        n = n -1
    return answer

def fact_recursion(n):
    """ Calcuate the factorial of n using recursion """
    print(" in fact_recursion with n = ", n)
    if n == 1:
        return 1
    else:
        return n * fact_recursion(n-1)

def main():
    n = int(input("What is n? "))
    print(f"Factorial of {n} with a loop is {fact_loop(n)}.")
    print(f"Factorial of {n} with recursion is {fact_recursion(n)}.")
    
if __name__ == "__main__":
    main()