$my_year = 2000;

if ( is_leap_year( $my_year ) ) {  
   print "$my_year is a leap year\n";
}
else {
   print "$my_year is not a leap year";
}

sub is_leap_year {        
   my $year = shift(@_);          # Shift off the year from the parameter list, @_
   return ((($year % 4 == 0) && ($year % 100 != 0)) ||
   ($year % 400 == 0)) ? 1 : 0;   # What is returned from the function
}