## Objective

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

## Difficulty

## Description

Consider the following array of numbers:

```
<?php
$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 ** multiply_all()** 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:

```
<?php
echo multiply_all([1, 5, 70, -2, -1, -0.5]), "\n";
echo multiply_all([2, 2, 2]), "\n";
echo multiply_all([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]), "\n";
var_dump(multiply_all([]));
```

## New file

Inside the directory you created for this course on PHP, create a new folder called **Exercise-16-Multiply-All** and put the .php solution files for this exercise within it.

## Solution

Let's start by defining the `multiply_all()`

function:

```
<?php
function multiply_all($nums) {
// Code to go here.
}
```

The `$nums`

parameter represents the array passed into the function that contains the number to be multiplied together.

First up, we'll deal with the special case, i.e. when `$nums`

is empty, where we have to return `NULL`

:

```
<?php
function multiply_all($nums) {
$len = count($nums);
if (!$len) {
return NULL;
}
}
```

Beyond the `if`

shown here, it's known for sure that `$nums`

contains some numbers. Likewise, we ought to multiply them all using a `for`

loop.

In this regard, we'll create a variable ** $product** to keep track of this product. Initially, it'll be equal to

`1`

since 1 is the multiplicative identity of numbers:```
<?php
function multiply_all($nums) {
$len = count($nums);
if (!$len) {
return NULL;
}
// $nums contains some numbers, so compute the product.
$product = 1;
}
```

Now, let's get done with the `for`

loop:

```
<?php
function multiply_all($nums) {
$len = count($nums);
if (!$len) {
return NULL;
}
// $nums contains some numbers, so compute the product.
$product = 1;
for ($i = 0; $i < $len; $i++) {
$product *= $nums[$i];
}
return $product;
}
```

And this completes the exercise.