PS.: please use code-tags for formatting your code!

OOps ... I got confused by the [] not shown due to missing code-tags :-(

Now here is some code (yours, however modified) with comments - and it works :-)

use strict;                                         # use this always.
+ no excuses.
use warnings;                                       # same with this.

my @params; my @charam; my @actual;                 # declare all your
+ variables!!
my $i; my $j;                                       # declare all your
+ variables!!

open FILE, "params.txt" or die "unable to open\n"; 
for($i=1,$j=1; <FILE>; $i++, $j++) { 
    chomp; 
    (@params[$i], @charam[$j]) = split(':');    # use $i and $j here, 
+not i and j!!!
    $actual[$i]=$charam[$j];                    # better use $actual[$
+i] instead of @actual[$i] (same on line above!)
    print "inside $actual[$i]\n"; 
} 
print "out side @actual\n";                         # it works, but gi
+ves an error as $actual[0] is undefined
close(FILE);
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