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 "cells": [
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "scientific-priest",
   "metadata": {},
   "outputs": [],
   "source": [
    "# This tutorial will introduce simple implementations of while loops\n",
    "# in Python."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "promising-witness",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "n = 4\n",
      "n! = 24\n"
     ]
    }
   ],
   "source": [
    "# Here's a while loop that calculates the factorial of n.  Start with n = 4\n",
    "# to make sure things are working properly.  The loop executes until n > 1.\n",
    "# That is, the the last iteration of the loop will occur when n = 2. (You\n",
    "# could actually let the while loop run until n = 1 since factorial*1 =\n",
    "# factorial).\n",
    "n = 4\n",
    "print('n =', n)\n",
    "factorial = 1\n",
    "while n > 1:\n",
    "    factorial = factorial*n\n",
    "    n = n - 1\n",
    "print('n! =', factorial)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "handed-curtis",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "n = 50\n",
      "n! = 30414093201713378043612608166064768844377641568960512000000000000\n"
     ]
    }
   ],
   "source": [
    "# Here's a more interesting factorial\n",
    "n = 50\n",
    "print('n =', n)\n",
    "factorial = 1\n",
    "while n > 1:\n",
    "    factorial = factorial*n\n",
    "    n = n - 1\n",
    "print('n! =', factorial)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "stone-surgeon",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "n! = 3.0414093201713376e+64\n"
     ]
    }
   ],
   "source": [
    "# We can force the number to be written in scientific notation while keeping\n",
    "# only some of the digits after the decimal point using:\n",
    "print('n! =', float(factorial))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "colonial-nickel",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "n = 170\n",
      "n! = 7.257415615307999e+306\n"
     ]
    }
   ],
   "source": [
    "# Here's a a crazy big number...\n",
    "n = 170\n",
    "print('n =', n)\n",
    "factorial = 1\n",
    "while n > 1:\n",
    "    factorial = factorial*n\n",
    "    n = n - 1\n",
    "print('n! =', float(factorial))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "underlying-cocktail",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Enter an integer: 17\n",
      "n = 17\n",
      "n! = 355687428096000.0\n"
     ]
    }
   ],
   "source": [
    "# Here's the factorial of a user-entered value.\n",
    "n = int(input(\"Enter an integer: \")) \n",
    "print('n =', n)\n",
    "factorial = 1\n",
    "while n > 1:\n",
    "    factorial = factorial*n\n",
    "    n = n - 1\n",
    "print('n! =', float(factorial))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "minus-publicity",
   "metadata": {},
   "outputs": [],
   "source": [
    "# Maybe you want to the user to be able to enter only integer numbers with\n",
    "# appropriate error messages. \n",
    "\n",
    "# See the nested control structure tutorial for an implementation of this\n",
    "# check.  That tutorial will also show you how to calculate the factorials\n",
    "# of a bunch of n values and then plot the results vs n."
   ]
  }
 ],
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