Course: JavaScript

Progress (0%)

# Exercise: Multiply All

Exercise 24 Very easy

Prerequisites for the exercise

1. JavaScript `for` Loop
2. All previous chapters

## Objective

Create a function to multiply all the numbers in a given array and return the product.

## Description

Consider the following array of numbers:

``var nums = [1, 5, 70, -2, -1, -0.5];``

If we multiply all the numbers together, we get the value `-350`.

In this exercise, you ought to create a function `multiplyAll()` that takes in an array of numbers and returns back their product.

If the array is empty, the value returned should be `null`.

Here are some examples of the usage of the function:

``multiplyAll([1, 5, 70, -2, -1, -0.5]);``
-350
``multiplyAll([2, 2, 2]);``
8
``multiplyAll([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);``
3628800
``multiplyAll([]);``
null

## New file

Inside the directory you created for this course on JavaScript, create a new folder called Exercise-24-Multiply-All and put the .html solution files for this exercise within it.

## Solution

To start with, we'll deal with the special case, i.e. when the given array is empty, where we have to return `null`:

``````function multiplyAll(arr) {
if (arr.length === 0) {
return null;
}
}``````

Proceeding forward, we lay out a variable `product` to hold the product of itself and the current number during each iteration of the loop.

In the end, this variable effectively holds the product of all the numbers in the array.

Altogether, we get to the following code:

``````function multiplyAll(arr) {
if (arr.length === 0) {
return null;
}

var product = 1;
for (var i = 0; i < arr.length; i++) {
product *= arr[i];
}

return product;
}``````

"I created Codeguage to save you from falling into the same learning conundrums that I fell into."

— Bilal Adnan, Founder of Codeguage