Increment operation code for string under PHP_PHP tutorial-PHP Tutorial-php.cn

Increment operation code for string under PHP_PHP tutorial

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Release： 2016-07-21 15:34:07

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A student asked a question:

Copy the code The code is as follows:

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

The output is:

Copy code The code is as follows:

ABCDEFGHIJKLMNOPQRSTUVWXYZAAABACADAEAFAGAHAIAJAKALAMANAOAPAQARAS…….

is What ?

In fact, it is very simple. There are instructions in the PHP manual, but I am afraid many people will not read the manual carefully chapter by chapter:

Copy code The code is as follows:

 
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 dealing with arithmetic operations on character variables, PHP follows Perl's habits instead of C's. For example, in Perl 'Z'+1 will get 'AA', while in C, 'Z'+1 will get '[' (ord('Z') == 90, ord('[') == 91). Note that character variables can only be incremented, not decremented, and only pure letters (a-z and A-Z) are supported.

That is, if:

Copy code The code is as follows:

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

and:

Copy code The code is as follows :

 
$name = "laruence"; 
--$name; //No effect, still "laruence" 

So, the reason for this problem is When $i = Z, ++$i becomes AA, and when comparing strings,
AA, BB, XX to YZ are all less than or equal to Z... so..

Author : laruence