###### caroline

6,974 Points# Need help with quiz question

In the quiz Working with Functions, the answer to the question 'What does this code display"? is apparently 321. I cannot for the life of me figure out how 321 is the answer.

For a start, if $output = $number . $output, it would echo

1 ""

after the first cycle, because $number = 1, and $output = "".

Or am I being really stupid?

If anyone could walk me through this I'd be really grateful. (Code pasted below.)

<?php

$numbers = array(1,2,3,4);

$total = count($numbers);

$sum = 0;

$output = "";

$i = 0;

foreach($numbers as $number) {

```
$i = $i + 1;
if ($i < $total) {
$output = $number . $output;
}
```

}

echo $output;

?>

## 4 Answers

###### Filipe Pacheco

**Full Stack JavaScript**Techdegree Student 21,413 Points

Hi, Caroline,

Remember that the foreach loop will loop through each array value. So if it has 4 values, it will loop 4 times. Let's try to go through the code each time the loop runs it. Remember the first line of code inside the foreach loop.

```
$i = 0;
foreach($numbers as $number) {
$i = $i + 1;
}
```

So running through it the first time, $i will be 0 + 1, so when the loop ends the first time, $i = 1. This value will keep stored in this variable for the next loop, so in the second loop, the code will be $i = 1 + 1; So now, $i is equal to 2. Again, this value will be stored in the variable $i. Now the third time, $i = 2 + 1;, which is equal to 3. Now the fourth time, $i = 3 + 1, which is 4. Since the array has only four values, the loop runs only 4 times. So now will know the first time, $i was equal to 1, the second time it was 2, the third was 3 and the fourth was 4.

Now we will go to the second line of code.

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

The if statement says to run the line of code inside it only if $i is less than the $total. Since $total = count($numbers);, it mean that $total is equal to 4, so the if statement says if($ i < 4). Which means it will run until 3. So the conde inside that statement will be executed only 3 times.

Now let's execute that code each time until 3, to see what happens.

In the first time , it will fetch the first value of the array, so $number will be equal to 1. Now the $output will be 1 concatenated to the previous output. Since this is the first loop, the output has no value, so $output = 1 + 0;

```
$number = 1;
$output = "";
$output = $number . $output;
$output = 1 . "";
$output = 1;
```

Now that it looped the first time, the value 1 was stored in the output for the next loop. Since it's now the second loop, it will fetch the second value from the array, which is 2, so now $number = 2 and $output = 1, if you concatenate them, $output will be 21.

```
$number = 2;
$output = 1;
$output = $number . $output;
$output = 1 . 2;
$output = 21;
```

Now for the third and last time, the value fetched will be 3, so $number = 3 and $output = 21. If you concatenate them, $output will be 321.

```
$number = 3;
$output = 21;
$output = $number . $output;
$output = 3 . 21;
$output = 321;
```

###### nfs

35,506 PointsAmazing explanation @filipepacheco.

###### caroline

6,974 PointsOK - I have now done my own homework (!) and found the answer here http://us2.php.net/manual/en/function.empty.php. The "" means that the variable is empty. My next question is - why use '"" instead of NULL or FALSE? Substituting NULL or FALSE also seems to work.

###### Filipe Pacheco

**Full Stack JavaScript**Techdegree Student 21,413 Points

I'm glad to know it helped.

That's, right. And yes, you can use null, or 0 (I'm not sure about the false), but It just means that the variable is empty. I'm still studying php, so I put inside the quotation marks because this is what I see most people usually doing. But anyways, in the first loop you can just ignore the concatenation to the output, since it's empty.

###### caroline

6,974 PointsThanks Felipe!

## caroline

6,974 Points## caroline

6,974 PointsHi Filipe

Thank you so much for taking the time to write such a detailed explanation - it's so helpful! I understand how the foreach loop works, and why the code only executes 3 times. I'm getting closer to understanding why we end up with 321, but I'm still confused about the $output variable.

What I don't understand is how: $output = 1 . "";

becomes

$output = 1;

I would have thought concatenating 1 and "" (ie 1 . "") would give us 1"". However, that's clearly not the case. Can you explain what those quotation marks are doing? Is it just because the $output variable can't be empty when it's declared? I suppose this would tie up with what you say about $output initially having 'no value'.