The for loop behaves differently depending on how the variable $i is declared. Consider the following two programs - 
#!/usr/local/bin/perl -w    #!/usr/local/bin/perl -w
use strict;                 use strict;             

my $i = 45;                 our $i = 45;

for $i (0..67) {            for $i (0..67) {
  last if $i == 10;           last if $i == 10;
  investigate();              investigate();
}                           }
print $i."\n";              print $i."\n";

sub investigate {           sub investigate {
  print "\$i=$i\n";           print "\$i=$i\n";    
}                           }

[download]
The difference is that the left program declares a my variable, while the right program declares an our variable.

However, when I run the programs, I get completely different behaviour inside the for loop:

45                         0
45                         1    
45                         2    
45                         3    
45                         4    
45                         5    
45                         6    
45                         7    
45                         8    
45                         9    
$i=45                      $i=45

[download]
Note that inside the for loop, the value of the top level my $i variable is not affected, while the global our $i variable gets temporarily affected. An interesting observation is made: Perl localizes the $i variable differently inside the for loop, depending on how $i is declared in the first place.

When the top level $i variable is declared as a my variable, the for loop is equivalent to -
my $i = 45;
for (0..67) {
  my $i = $_;
  ...
}

[download]
When the top level $i variable is declared as an our variable, the for loop is equivalent to -
our $i = 45;
for (0..67) {
  local $i = $_;
  ...

[download]

In reply to Re: "for" surprise by Roger
in thread "for" surprise by fletcher_the_dog

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.