The problem is that the list ($a .. ++$a) is not evaluating a list like you think it is. It is not doing: 
$start = $a;
$end = ++$a;
for ($_ = $start; $_ <= $end; $_++) { ... }

[download]
But rather, it is evaluating its endpoints, and then constructing the list from that. That is the cause of your problem: 
for (++$x .. $x++ . $x) { ... }
# starting at ++$x
# ending at $x++ . $x
# THE END HAS MODIFIED THE START

[download]
You can witness a similar result from: 
print ++$x, ++$x, ++$x;  # 333

[download]
You see, the arguments to a function aren't copies of the variables, but rather aliases -- by modifying ONE of the $x's, you've modified the others as well.

Knowing this, the output of this program makes sense to me: 

$x = 3;
print ++$x/$x--;  # 3/4 => 0.75

[download]
Why is that? Well, the numerator is ++$x, and the denominator is $x--; but in subtracting 1 from $x in the denominator, we have now altered the numerator back to its original state!

I've worked out a solution to your 1 .. 12 loop, then. 

for (++$x .. $x++ . $x--) { ... }
# or
for (++$....$.++.$.--) { ... }

[download]
See if you can work out why the starting point is 1.

japhy -- Perl and Regex Hacker

In reply to Re: Re: Re: For loop problem by japhy
in thread For loop problem by srawls

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.