It looks like you're trying to concatenate the results of $y + 2 to the previous string and assign the entire result to $x. If that's the case, you need to use the concatenation operator "." (see perlop) or join, not the comma operator. Your current code assigns "Expected value is" to $x and then sums $y + 2 but does not use the result of the summation. Try one of these:

$x = "Expected value is " . ($y + 2);
$x = join( ' ', "Expected value is", $y + 2 );
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Update: Note that "." and "+" have equal precedence (see perlop), so the parentheses are needed to ensure that the sum is concatenated to the string, not just the value of $y.

$x = sprintf "Expected value is %d", $y + 2;
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You can also make concatenation implicit by getting the sum to evaluate inside interpolating quotes:

my $x = "Expected value is ${\($y + 2)}";
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If you're going to do that at least use the slightly more symmetrical @{[ $y + 2 ]}.

Come on people! Aesthetics! We want eye-pleasing line noise.

:)

that thing seems to be working. Thanks for the reply.

If you can answer "what are you trying to achieve", we may be able to answer your question. If you are simply declaring two initialised variables then:

my $x = "Expected value is";
my $y = 2;
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is the way to do it. However I'd expect $y would cause trouble in your code in that case - you do include use strict; in your script don't you?

If you are trying to increment $y and concatenate the result on to the end of the string then you need something like:

my $x = "Expected value is " . ($y + 2);
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Note that the () are required.