Why doesn't this code simply print letters A to Z?

Question 1

<?php
for ($i = 'a'; $i <= 'z'; $i++)
    echo "$in";

This snippet gives the following output (newlines are replaced by spaces):

a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw bx by bz ca cb cc cd ce cf cg ch ci cj ck cl cm cn co cp cq cr cs ct cu cv cw cx cy cz da db dc dd de df dg dh di dj dk dl dm dn do dp dq dr ds dt du dv dw dx dy dz ea eb ec ed ee ef eg eh ei ej ek el em en eo ep eq er es et eu ev ew ex... on to yz

Question 2

From the docs:

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.

From Comments:-
It should also be noted that <= is a lexicographical comparison, so 'z'+1 ? 'z'. (Since 'z'+1 = 'aa' ? 'z'. But 'za' ? 'z' is the first time the comparison is false.) Breaking when $i == 'z' would work, for instance.

Example here.

Question 3

Here's what worked best for me when trying to script this (in case anyone else comes across this like I did):

$ pecl -d php_suffix=5.6 install <package>
$ pecl uninstall -r <package>

$ pecl -d php_suffix=7.0 install <package>
$ pecl uninstall -r <package>

$ pecl -d php_suffix=7.1 install <package>
$ pecl uninstall -r <package>

The -d php_suffix=<version> piece allows you to set config values at run time vs pre-setting them with pecl config-set. The uninstall -r bit does not actually uninstall it (from the docs):

vagrant@homestead:~$ pecl help uninstall
pecl uninstall [options] [channel/]<package> ...
Uninstalls one or more PEAR packages.  More than one package may be
specified at once.  Prefix with channel name to uninstall from a
channel not in your default channel (pecl.php.net)

Options:
  ...
  -r, --register-only
        do not remove files, only register the packages as not installed
  ...

The uninstall line is necessary otherwise installing it will remove any previously installed version, even if it was for a different PHP version (ex: Installing an extension for PHP 7.0 would remove the 5.6 version if the package was still registered as installed).

Question 4

There are invisible characters here that alter how the code is displayed. In Intellij these can be found by copy-pasting the code into an empty string (""), which replaces them with Unicode escapes, removing their effects and revealing the order the compiler sees.

Here is the output of that copy-paste:

"class Mu202E{public static void main(String[]au202D){System.out.print(new char[]n"+
        "{'H','e','l','l','o',' ','W','o','r','l','d','!'});}}   "

The source code characters are stored in this order, and the compiler treats them as being in this order, but they're displayed differently.

Note the u202E character, which is a right-to-left override, starting a block where all characters are forced to be displayed right-to-left, and the u202D, which is a left-to-right override, starting a nested block where all characters are forced into left-to-right order, overriding the first override.

Ergo, when it displays the original code, class M is displayed normally, but the u202E reverses the display order of everything from there to the u202D, which reverses everything again. (Formally, everything from the u202D to the line terminator gets reversed twice, once due to the u202D and once with the rest of the text reversed due to the u202E, which is why this text shows up in the middle of the line instead of the end.) The next line's directionality is handled independently of the first's due to the line terminator, so {'H','e','l','l','o',' ','W','o','r','l','d','!'});}} is displayed normally.

For the full (extremely complex, dozens of pages long) Unicode bidirectional algorithm, see Unicode Standard Annex #9.

Question 5

Once you return from a method, you return to the method that called the method in the first place. Any statements you place after a return would be meaningless, as that is code that you can't reach without seriously violating the program counter (may not be possible in Java).

Question 6

Never used any of those, but they look interesting..

Take a look at Gearman as well.. more overhead in systems like these but you get other cool stuff :) Guess it depends on your needs ..

Why doesn't this code simply print letters A to Z?

Answers

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