Objective

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

Difficulty

Very easy

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([]));
-350 8 3628800 NULL
View Solution

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.