Getting Unexpected Result in For Loop - php

Question

I have this function ...
public function getGroupName($no_of_participant) {
$groupNameArry = array();
$groupNumber = 0;
for($i = 0; $i <= $no_of_participant/2; $i++) { // loop for rows
for($letter = 'A'; $letter <= 'Z'; $letter++) { // loop for columns
if($groupNumber <= $no_of_participant/2) {
if($i == 0) {
$groupNameArry[$groupNumber] = $letter;
} else {
$groupNameArry[$groupNumber] = $letter.$i;
}
$groupNumber++;
}
}
}
return $groupNameArry;
}
The expected Result is
A-Z and then A1,B1,C1,D1 ....
But unexpectedly getting
A-Z and then AA, AB, AC ...
I am calling this function like as
$groupNameArry = $this->getGroupName(MAX_ALLOWED_PARTICIPANT);
where maximum allowed participant value is 100. what is wrong? Please help!

Answer 1

$letter is a string.
When $letter becomes 'Z', the condition $letter <= 'Z' is TRUE and it runs what you expect to be the last iteration.
After this iteration $letter++ increments 'Z' and it becomes 'AA'. This is how PHP handles ++ on strings.
The increment operator turning 'Z' into 'AA' is even given as example in the documentation of the increment operators (See Example #1).
Then the condition $letter <= 'Z' is still TRUE and it runs more iterations with $letter having the values 'AA', 'AB', 'AC' a.s.o.
The PHP way to iterate from 'A' to 'Z' is to use foreach on a range():
foreach (range('A', 'Z') as $letter) {
echo($letter);
}
echo("\nDone.");
The output is:
ABCDEFGHIJKLMNOPQRSTUVWXYZ
Done.

Answer 2

In you code $i = 0 in every loop !!
This fixes your issue.
/**
* Get group name
*
* #param int $no_of_participant
* #return string
*/
public static function getGroupName(int $no_of_participant)
{
$groupNameArry = array();
$groupNumber = 0;
$letters = range('A', 'Z');
foreach ($letters as $letter) {
for ($i = 0; $i <= $no_of_participant / 2; $i++) {
if ($i == 0) {
$groupNameArry[$groupNumber] = $letter;
} else {
$groupNameArry[$groupNumber] = $letter . $i;
}
$groupNumber++;
}
}
return $groupNameArry;
}