PHP string increment operation code

Some students asked a question:

 
<?php 
for($i = 'A'; $i <= 'Z'; $i++) { 
echo $i; 
} 
//What is the output?

The output is:

 
ABCDEFGHIJKLMNOPQRSTUVWXYZAAABACADAEAFAGAHAIAJAKALAMANAOAPAQARAS ... . 

Why?

It's actually quite simple. There are instructions in the PHP manual, but I'm afraid that many people will not read the manual carefully chapter by chapter:

 
PHP follows Perl's convention when dealing with arithmetic operations on character variables and not C's. For example, in Perl  ' Z'+1 turns into  ' AA', while in C  ' Z'+1 turns into  ' [ '  ( ord( ' Z') == 90, ord( ' [ ' ) == 91 ). Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported. 

When it comes to arithmetic on character variables, PHP follows Perl's conventions, not C's. For example, in Perl 'Z'+1 will get 'AA', while in C 'Z'+1 will get' [' (ord('Z') == 90, ord(' [') == 91).

That is, if:

 
$name = "laruence"; 
++$name; //Will be "laruencf"

And:

 
$name = "laruence"; 
--$name; //It doesn't matter. It's still "laruence."

So, the reason for this problem is that when $I = Z, ++$I becomes AA, and when strings are compared,
AA,BB,XX up to YZ are all less than or equal to Z... So..

Author: laruence