Here are the rules about IN OUT parameters:

► A formal IN OUT parameter acts like an initialized variable.

► An actual IN OUT parameter must be a variable.

► An actual IN OUT parameter passes a copy of its value to the formal parameter when entering the procedure or function.

► An actual IN OUT parameter will receive a copy of the value from the formal parameter at the end of the procedure or function.

Here is good example of a procedure with IN OUT parameters:

SQL> CREATE OR REPLACE PROCEDURE SWAP_TEST AS

2 A NUMBER := 3;

3 B NUMBER := 8;

4 PROCEDURE MY_SWAP(X IN OUT NUMBER,Y IN OUT NUMBER) AS

5 T NUMBER;

6 BEGIN

7 T := X;

8 X := Y;

9 Y := T;

10 END MY_SWAP;

11 BEGIN

12 MY_SWAP(A,B);

13 DBMS_OUTPUT.PUT_LINE('A = ' || TO_CHAR(A));

14 DBMS_OUTPUT.PUT_LINE('B = ' || TO_CHAR(B));

15 END;

16 /

SQL> EXECUTE SWAP_TEST;

A = 8

B = 3