$#array is the index of the last element. pop shortens the array. In your condition, you have 
$index < $#array + 1

[download]
while in your body, you both increase $index and decrease $#array. So, after printing 5, $index is no longer less than $#array + 1, and hence the loop terminates.

Why not 

my @array = (1 .. 9);
while (@array) {
    my $last = pop @array;
    print "$last\n";
}

[download]
Or some alternatives: 
my @array = reverse (1 .. 9);
print "$_\n" for @array;

my @array = (1 .. 9);
my $index = $#array;
while ($index >= 0) {
    print $array[$index], "\n";
    $index--;
}

my @array = (1 .. 9);
for (my $index = $#array; $index >=0; $index--) {
    print $array[$index], "\n";
}

[download]

In reply to Re: $#array issue by JavaFan
in thread $#array issue by biohisham

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.