Ampersand in PL/SQL

Hello There,

        I typed the following PL/SQL block in a file.

declare

   zzz number(5);
   aaa number(5);
begin

   select sal into zzz from emp where empno = &aaa;    if (zzz > 2000) then

      update emp set sal = zzz + 10 where empno = aaa;    else

      update emp set sal = zzz + 500 where empno = aaa;    end if;
   commit;
end;
/

        At the SQL prompt, I started the file.

SQL> start vm_12.sql;
Enter value for aaa: 7369
old 5: select sal into zzz from emp where empno = &aaa; new 5: select sal into zzz from emp where empno = 7369;

PL/SQL procedure successfully completed.

SQL> select sal, empno from emp;

       SAL EMPNO
---------- ----------

       800       7369
      1600       7499
      1250       7521
      2975       7566
      1250       7654
      2850       7698
      2450       7782
      3000       7788
      5000       7839
      1500       7844
      1100       7876

       SAL      EMPNO


---------- ----------

       950       7900
      3000       7902
      1300       7934

14 rows selected.

        Salary(800) for empno 7369 is not changed. Is ampersand allowed in PL/SQL ? If so, why the salary is not being updated. When I invoke sqlplus, the following information is displayed on my screen.  

Command Prompt: sqlplus /

SQL*Plus: Version 3.0.11.1.2 - Production on Fri Apr 14 00:07:56 1995

Copyright (c) Oracle Corporation 1979, 1992. All rights reserved.

Connected to:
ORACLE RDBMS V6.0.36.0.1, transaction processing option - Production PL/SQL V1.0.34.2.1 - Production