@array=(2, 3, 1, 0);
foreach (sort @array){
  print "$_ - ";
}
print "\n";
print join " - ", @array;
print "\n";
@array = sort @array;
print join " - ", @array;

__END__
Output:
0 - 1 - 2 - 3 - (printed in loop)
2 - 3 - 1 - 0   (after loop, still unsorted)
0 - 1 - 2 - 3   (after sorting, now sorted)