While loop and diamond operator in Perl - perl

Question

I am trying to input a text file to Perl program and reverse its order of lines i.e. last line will become first, second last will become second etc. I am using following code
#!C:\Perl64\bin
$k = 0;
while (<>){
print "the value of i is $i";
#array[k] = $_;
++$k;
}
print "the array is #array";
But for some reason, my array is only printing the last line of the text file.
Any suggestions?

Answer 1

Typically, rather than keep a separate array index, perl programs use the push operator to push a string onto an array. One way to do this in your program:
push #array, $_;
If you really want to do it by array index, then you need to use the following syntax:
$array[$k] = $_;
Notice the $ rather than # in front. This tells perl that you're dealing with a single element from the array, not multiple elements. #array gives you the entire array, while $array[$k] gives you a single element. (There is a more advanced topic called "slices," but let's not get into that here. I will say that #array[$k] gives you a slice, and that isn't what you want here.)
If you really just want to slurp the entire file into an array, you can do that in one step:
#array = ( <> );
That will read the entire file into #array in one step.
You might have noticed I omitted/ignored your print statement. I'm not sure what it's doing printing out a variable named $i, since it didn't seem connected at all to the rest of the code. I reasoned it was debug code you had added, and not really relevant to the task at hand.
Anyway, that should get your input into #array. Now reversing the array... There are many ways you could do this in perl, but I'll let you discover those yourself.

Answer 2

Instead of:
#array[k] = $_;
you want:
$array[$k] = $_;
To reference the scalar variable $k, you need the $ on the front. Without that it is interpreted as the literal string 'k', which when used as an array index would be interpreted as 0 (since a non-numeric string will be interpreted as 0 in a numeric context).
So, each time around the loop you are setting the first element to the line read in (overwriting the value set in the previous iteration).
A few other tips:
#array[ ] is actually the syntax for an array slice rather than a single element. It works in this case because you are assigning to a slice of 1. The usual syntax for accessing a single element would be $array[ ].
I recommend placing 'use strict;' at the top of your script - you would have gotten an error pointing out the incorrect reference to $k
Instead of using an index variable, you could push the values onto the end of the array, eg:
while (<>) {
push #array, $_;
}

Answer 3

Accept input until it finds the word end
Solution1
#!/usr/bin/perl
while(<>) {
last if $_=~/end/i;
push #array,$_;
}
for (my $i=scalar(#array);$i>=0;$i--){
print pop #array;
}
Solution2
while(<>){
last if $_=~/end/i;
push #array,$_;
}
print reverse(#array);