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Create factorial.js
This program calculates and displays the factorial for a user-input number.
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52
maths/factorial.js
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52
maths/factorial.js
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/*
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author: PatOnTheBack
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license: GPL-3.0 or later
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Modified from:
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https://github.com/TheAlgorithms/Python/blob/master/maths/factorial_python.py
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This script will find the factorial of a number provided by the user.
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More about factorials:
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https://en.wikipedia.org/wiki/factorial
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*/
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function calc_range(num) {
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// Generate a range of numbers from 1 to `num`.
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"use strict";
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var i = 1;
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var range = [];
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while (i <= num) {
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range.push(i);
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i += 1;
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}
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return range;
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}
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function calc_factorial(num) {
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"use strict";
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var factorial;
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var range = calc_range(num);
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// Check if the number is negative, positive, null, undefined, or zero
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if (num < 0) {
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return "Sorry, factorial does not exist for negative numbers.";
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}
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if (num === null || num === undefined) {
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return "Sorry, factorial does not exist for null or undefined numbers.";
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}
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if (num === 0) {
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return "The factorial of 0 is 1.";
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}
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if (num > 0) {
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factorial = 1;
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range.forEach(function (i) {
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factorial = factorial * i;
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});
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return "The factorial of " + num + " is " + factorial;
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}
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}
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// Run `factorial` Function to find average of a list of numbers.
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var num = prompt("Enter a number: ");
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alert(calc_factorial(num));
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