Why not use a for loop like so:

use warnings;
use strict;

  my @alpha = qw(a b c d e f);

  my @location = qw(0 2 4);

   print $alpha[$_+1] for @location; # prints bdf
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  my @alpha = qw(a b c d e f);

  my @location = qw(0 2 4 6 8 10 12);

  for (@location){
     print $alpha[$_+1] if defined $alpha[$_+1];
  }
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+$1 should be +1. Other than that, the code should work.

If it still doesn't, the error is probably in the preceding part that you have not shown (where you initialize the variables).

No +1 does no work either , but I got the answer we can do it like  $words[++$tst_num_temp[$c2] instead of $words[$tst_num_temp[$c2]+$1] . It works . thanks anyways

"No +1 does no work either"

Sure it does:

use warnings;
use strict;

#               0   1   2   3   4   5   6   7
#               '   '   '   '   '   '   '   '
my @words = qw(aaa bbb ccc ddd eee fff ggg hhh);
my @tst_num_temp = qw(0 4 6);

my $c2 = 0;
my @tst_num;

while ($c2<=$#tst_num_temp) {
  $tst_num[$c2]=$words[$tst_num_temp[$c2]+1];
  $c2++;
}

print "@tst_num\n";
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...prints:

bbb fff hhh
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"but I got the answer we can do it like $words[++$tst_num_temp[$c2]"

You can, and it will get you the exact same result for @tst_num as the +1 method. But in addition to that it will also modify @tst_num_temp, which you should be aware of in case the following code continues to use that variable.

In any case, consider using a for loop like 2teez suggested, it's much nicer compared to a while loop with manually incremented index.