Use strict and warnings. Do not use global variables. 
#!/usr/bin/perl
use warnings;
use strict;

use Date::Calc qw ( Monday_of_Week Add_Delta_Days );

sub weekToDays {
    my $week = shift;
    my $year = shift;

    my ($year2, $month, $day) = Monday_of_Week($week, $year);

    my ($y, $m, $d) = Add_Delta_Days( Monday_of_Week($week, $year), 6)
+; # Not $year2 here!

    return "$day/$month/$year2 to $d/$m/$y";
}
print "First week of 2013: ".weekToDays ( 1, 2013) ."\n" ;
print "Second week of 2013: ".weekToDays ( 2, 2013) ."\n" ;

[download]

Output: 

First week of 2013: 31/12/2012 to 6/1/2013
Second week of 2013: 7/1/2013 to 13/1/2013

[download]
Update: You can even avoid calling the function again when you already know the result:
my ($y, $m, $d) = Add_Delta_Days($year2, $month, $day, 6);

[download]
لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re: big bug in Date::Calc? by choroba
in thread big bug in Date::Calc? by luca76

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.