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how does this function calculate to 321

I had this question in a quiz, I got the answer wrong and it's really stressing me how this function works.. I know the answer is 321 but can someone explain step by step how it becomes 321 :/ totally makes no sense in my head! :/

$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;

Ok

The for loop looks at all the numbers in the numbers array. This means it will repeat anything within the block as many times as the array has entries. Then the value of i is set to i plus 1 After this there will be a check if the value of i is smaller than the value of total. If so, output will be number plus output pasted behid it ( not calculus +)

first run (1 out of 4) because the array has 4 entries) i = 0 -> becomes 1. is i (1) smaller than total(4) in this case i is smaller than total. output now becomes 1 (see number . output as -> numberoutput)

then the loop goes again through same process (run 2 out of 4) i = 1 -> becomes 2 i (2) is still smaller than total(4) output becomes number(2).output(1) -> 21

loop goes through process again (run 3 out of 4) i = 2 -> becomes 3 i(3) is still smaller than total(4) output becomes number(3).output(21) -> 321

loop goes through process one last time however i(4) is equal to total(4) so it stops

sorry for million edits trying to get this crazy format good but i keep failing

2 Answers

Kevin Korte
Kevin Korte
28,103 Points

Sure.

So $numbers is an array of 1,2,34.

$total is a number that is the size of the array, which is 4. There are 4 numbers in the $numbers array.

$sum is zero, easy.

$output is just an empty initialized variable we are going to store our answer in

$i is our "iterator", we will use to keep track of our position in the loop.

Okay, the foreach loop. It's going to take each number in our array, and run the loop through it. Whatever number it's working on, will be stored in the temp variable $number. It's very common to see this design patter. Your array variable is plural, $numbers, because it's an array of values, but inside we are working on only one value of the array, so we use the singular version of the word, or $number.

So, the first line of code says: Foreach value in our number array, store it as a number. Sound round one.

Foreach(1,2,3,4 as 1) {

$i = 0 + 1;

if $i is less than $total (which is 4, remember) this will evaluate to true, so run the if statement.

$output = 1 concatenated to $output which is empty at this point.

and run the next foreach loop

Foreach(1,2,3,4 as 2) {

$i = 1+1;

if $i is less than $total (which is 4, remember) this will evaluate to true, so run the if statement.

$output = 2 concatenated to $output, which has the value of 1 right now. It's added to the front, so $output now equals 21

and again

Foreach(1,2,3,4 as 3) {

$i = 2+1;

if $i is less than $total (which is 4, remember) this will evaluate to true, so run the if statement.

$output = 3 concatenated to $output (remember, it's now 21). Now $output is 321

and again

Foreach(1,2,3,4 as 4)

$1 = 3+1;

if $i is less than $total (which is 4, remember) this will evaluate to true. BUT WAIT. $i = 4, and $total = 4. So $i is not less than $total, it's equal to total. So we DO NOT RUN this if statement. Skip it and move on.

Well that's the end of our foreach loop, we've ran through the entire array of numbers, so all that's left to do is echo $output, which is ..... 321

thanks, both good answers but i had to mark one, there's no favorite :p