How doe's push and pop work? I have been reading alot about perl but I don't understand how this script Works.I have been trying to break it down one by one but i still don't get it Can some help.


#!/usr/bin/perl
# stacks.plx
use warnings;
use strict;

my $hand;
my @pileofpaper = ("letter", "newspaper", "gas bill", "notepad");

print "Here's what's on the desk: @pileofpaper\n";

print "You pick up something off the top of the pile.\n";
$hand = pop @pileofpaper;
print "You have now a $hand in your hand.\n";

print "You put the $hand away, and pick up something else.\n";
$hand = pop @pileofpaper;
print "You picked up a $hand.\n";

print "Left on the desk is: @pileofpaper\n";

print "You pick up the next thing, and throw it away.\n";
pop @pileofpaper;

print "You put the $hand back on the pile.\n";
push @pileofpaper, $hand;

print "You also put a leaflet and a bank statement on the pile.\n";
push @pileofpaper, "leaflet", "bank statement";

print "Left on the desk is: @pileofpaper\n";

Imagine your stack goes from left to right like this:

1 2 3 4

pop($stack) removes the 1 from the left of the stack and you're left with

2 3 4

push($stack, 5) pushes 5 on to the left of the stack so you're left with

5 2 3 4

Normally people think of stacks vertically with what I've called the left at the top.

HTH

--
Charlie Harvey's website - linux, perl, java, anarchism and punk rock: http://charlieharvey.org.uk