Whats with the autoincrementation of a string

[bingalee]

Im trying to figure this out but I dont get it. Here's the code

#!/usr/bin/perl
use warnings;
$a = "A9"; print ++$a, "\n";
$a = "bz"; print ++$a, "\n";
$a = "Zz"; print ++$a, "\n";
$a = "z9"; print ++$a, "\n";
$a = "9z"; print ++$a, "\n";

OUTPUT

>perl auto2.plx
B0
ca
AAa
aa0
10
>

I get the first two outputs, A turns to B and 9 to 0.

But how does "Zz" become "AAa", "z9" become "aa0" and so on.. *confused*

[space_monk]

Note that the incrementation sequences are

0..9 => 0 + carry|1 i.e  10
A..Z => A + carry|A i.e. AA
a..z => a + carry|a i.e  aa

bz => ca

wrapping the z->a gives a carry to the b next in Lower a..z is c.

Zz => AAa

wrapping the z->a gives a carry to the Z next in Upper case A..Z is AA.

z9 => aa0

incrementing 9 wraps round to zero, passing a carry up to the z. Next up from z is aa

9z => 10

tricked you!! - string autoincrement only works on patterns matching regex /^[a-zA-Z]*[0-9]*\z/, this doesn't match that pattern, so treats leading number(s) as the (numeric?) value and increments that. 9 goes to 10 :-)



Read more... (39 Bytes)

[bingalee]

ok, so what about something that doest end with a "z" or a "9". Like will "zc" become "aad?"

[choroba]

No, "zc" will become "zd". Similarly, 93 + 1 = 94, not 104.

[LanX]

Think of every position as a wheel in a mechanical counter.

There are three kinds of wheels 0-9, a-z and A-Z which can be independently be chosen for each position.

Clearer now? =)

edit

perlop

       the increment is done as a string, preserving
       each character within its range, with carry:

           print ++($foo = '99');      # prints '100'
           print ++($foo = 'a0');      # prints 'a1'
           print ++($foo = 'Az');      # prints 'Ba'
           print ++($foo = 'zz');      # prints 'aaa'

 

[space_monk]

Not quite independently. Any numeric wheels must be at the back.

e.g. 'Aa00' will work, '00Aa' won't.

[LanX]

Sure, anything with leading digits which isn't a proper number is dealt by atoi in numeric context, IIRC that's due to some C legacy.

  DB<109> @a=a..c
 => ("a", "b", "c")

  DB<110> $a["  1x"]
 => "b"

plz note: only with no warnings!