PL/pgSQL variables

DO $$
declare
/*
 * -->counter is variable and integer is type data
 * -->first_name is variable and varchar is type data
 * -->last_name is variable and varchar is type data
 * -->payment is variable and numeric is type data
 */
   counter    INTEGER := 1;
   first_name VARCHAR(50) := 'Rahmad';
   last_name  VARCHAR(50) := 'Nasution';
   payment    NUMERIC(11,2) := 20.5;
BEGIN
   RAISE NOTICE '% % % has been paid % USD', counter, first_name, last_name, payment;
END $$;