plpgsql Integer Concat To String

Hi,

I want to concatenate a it counter to a string in a loop in plpgsql.
DECLARE
counter integer := 1;
IdSet char : = 'UniqueId'
IdForEachRun varchar;
BEGIN

IdForEachRun := IdSet || counter;(PROBLEM HERE)
--Or IdForEachRun := IdSet + counter;(PROBLEM HERE)
While condition LOOP

Insert into Table values(IdForEachRun, ......)

counter := counter + 1;
IdForEachRun := IdSet || counter;(PROBLEM HERE)
--Or IdForEachRun := IdSet + counter;(PROBLEM HERE)
END LOOP

END
Language 'plpgsql'

Thanks in advance.

Paul Puneet