Thank you, sivaratna, for having updated your post with code tags. This is now much more legible.

We really need some information about the contents of the @prdct and @prdct1 arrays to figure out what you are trying to do and why, as you state, you're not entering the inner while loop.

I agree with stevieb that you should have:

use strict;
use warnings;
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at the top of your program and declare all the variables that you are using (using the my built-in).

Although this is not your main problem, please note that:

for ( $i = 0 ; $i <= $#res ; $i++ ) {
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can be written in a more idiomatic way:

for my $i (0..$#res) {
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or even better:

for my $thing (@res) {
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but it is not clear to me if this latter version would work in you specific case.

Also, you don't need:

        else {
        }
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If you don't need an else clause, just don't put it.

But these are minor things, please let us know what data you have as input and want you want to do with it. We need that to better help you.