Why isn't this simple Perl push/pop program working?

Question

I'm reading the Llama (Learning Perl) book, and working on the exercises. And for this exercise: Write a program that reads a list of strings on separate lines until end-of-input and prints out the list in reverse order. [. . .] Well, I already figured out a simpler approach (I remembered you could use `reverse` on arrays... Perl is so... awesome so far), but I am wondering why this one isn't working. ``` #!/usr/bin/perl use 5.010; chomp(@strings = <STDIN>); foreach (@strings){ push @revstrings, $_; } while($i++ <= scalar @revstrings){ say pop @revstrings; } ``` It goes like this: $ ./first one two three [^D] three two $ the output is the same if I change the `<=` in the while loop to just `<`.

Accepted Answer

You'll never get past halfway... Each time through that last iteration, you'd get:

- `$i++` means that `$i` will increase by one;

- `pop @revstrings` will mean that `scalar @revstrings` will decrease by one.

They'll meet in the middle, when `$i++` just exceeds half the original `@revstrings` length.

Actually, the `$i++` is unnecessary, since `scalar @revstrings` will be zero when the array is empty, so you just need:

```
while(scalar @revstrings){
    say pop @revstrings;
}
```

Why isn't this simple Perl push/pop program working?

Solution

Problem