print "\nlist as a stack (after push to top): \n";
@words=();
push (@words, 'NS');
push (@words, 'IE');
push (@words, 'Opera');

for ($index = 0; $index<@words; $index++) {
	print "$words[$index]\n";
}

print "\nafter pop (from stack / top of stack)\n";
$x = pop (@words);
for ($index = 0; $index<@words; $index++) {
	print "$words[$index]\n";
}
print "the poped element is $x\n";

print "\nafter shift (from stack / bottom of stack)\n";
$x = shift (@words);
for ($index = 0; $index<@words; $index++) {
	print "$words[$index]\n";
}
print "the shifted element is $x\n";

print "\nadd element to (stack / bottom of stack)\n";
unshift (@words, "Mosaic");
for ($index = 0; $index<@words; $index++) {
	print "$words[$index]\n";
}