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PHP Build a Basic PHP Website Listing and Sorting Inventory Items Working with Functions

Can anyone tell me why the below code outputs the array in reverse?

Quiz Question 1 of 8 What does the following code display?

$numbers = array(1,2,3,4);
$total = count($numbers);
$sum = 0;
$output = "";
$loop = 0;

foreach($numbers as $number) {
    $loop = $loop + 1;
    if ($loop < $total) {
        $output = $number . $output;
    }
}

echo $output;

?>

Thanks all

Edited to add markdown

2 Answers

Jennifer Nordell
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STAFF
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher

Hi there, Matt Nickolls! I took the liberty of adding some markdown to your question so that it is a bit easier to read. Sure, I can guide you through why this is the case.

The first thing to keep in mind is that $output is an empty string and we're going to be concatenating it onto the end of another string each iteration.

Here's the loop part:

foreach($numbers as $number) {
    $loop = $loop + 1;
    if ($loop < $total) {
        $output = $number . $output;
    }
}

At the first iteration, $number will be equal to 1. $loop will also be set to 1. The $total variable holds the number of numbers in that array. So it is 4 and will not change. Is 1 less than 4? Yes, it is. So take the empty string and set it to the $number concatenated with the empty string and overwrite $output. So now $output is the result of "1" concatenated with "", which gives $output the value of "1".

Now onto the second iteration. The $number is now 2 and $loop is now 2. Is 2 less than 4? Yes, it is. So take $output which is now the string "1" and set it equal to the number (which is 2) concatenated with $output ("1") on the end. Now $output is equal to "21". Because we're taking the number and concatenating the previous version of $output on the end.

Third iteration. $number is now 3. $loop is 3. Is 3 less than 4? Yup. $output is "21". So we take the number (which is 3) and concatenate "21" onto the end of 3 and overwrite $output. The $output variable now has a value of "321".

Final iteration. $number is now 4. $loop is 4. Is 4 less than 4? Nope. Loop ends here.

So then we echo out the value of $output which is "321".

Hope this helps! :sparkles:

edited for additional information

It's the order of the concatenation that's important here. If this line:

$output = $number . $output;

had instead been...

$output = $output . $number;

then it would have echoed out "123" :smiley:

Thanks Jennifer, makes total sense.