The whole idea of a foreach my $x (@arr){} iterator is so that you don't have to know the number of elements in @arr to process each one. In many languages like C, you have to setup something like:
for (i=0;i<=max;i++){..do something with x[i], etc..}.

In Perl, the foreach loop causes $x to become each thing in the array successively without: a)modifying the size of @arr (the $x value can be use to modify a value in @arr); b) needing a subscript and c)perhaps more importantly, you don't have to worry about the ending condition being: i<=max or i<max! "off-by-one" is a VERY common error.

If you want to keep track of how many x's there have been processed so far, then something like this is a better way to go because the looping construct doesn't depend upon the $count value, meaning that you won't "overflow" the array bounds even if your count should have started at 0 instead of 1 or maybe a --$count vs $count++ boo-boo: 

my @arr =(10,11,12);
my $count =1;
foreach my $x (@arr)
{
   print $count++," $x\n";
}
#prints
#1 10
#2 11
#3 12

[download]
If you are going to actually reduce the size (num of elements) in @arr instead of just iterating over each element, then use a "while" loop. The following processes pairs of things from @tokens and removes them from @tokens as it does so. 
while (@tokens)
{
   my ($x, $y) = splice(@tokens,0,2);
   .....use $x and $y to do something...
   ..next loop causes another pair of $x, $y to be
     used if there are any left in @tokens
}

[download]
Update: To simplify the above to one shift (instead of 2 using splice()), this is completely legal although not a normal situation: 
#!/usr/bin/perl -w
use strict;

my @arr = ( 11, 12, 13, 14 );

while (@arr)
{
   my $x = shift(@arr);
   print "this item=$x #left in arr ".@arr."\n";
}
=prints
this item=11 #left in arr 3
this item=12 #left in arr 2
this item=13 #left in arr 1
this item=14 #left in arr 0
=cut

[download]

In reply to Re: Why does a full iteration over array & shift is not emptying the array by Marshall
in thread Why does a full iteration over array & shift is not emptying the array by Anonymous Monk

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.