How To Use "IN" Parameter Properly? - Oracle DBA FAQ - Creating Your Own PL/SQL Procedures and Functions

Here are the rules about IN parameters:

• A formal IN parameter acts like constant. It can not be assigned with new values.
• An actual IN parameter can take a value or a variable.
• An actual IN parameter is passed by reference to the specified value or the value of the specified variable.
• An actual IN parameter will not receive any value from the formal parameter.

Here is good example of a procedure with an IN parameter:

SQL> CREATE OR REPLACE PROCEDURE WELCOME AS
  2    SITE CHAR(80) := 'FYICenter.com';
  3    PROCEDURE WELCOME_PRINT(S IN CHAR) AS
  4    BEGIN
  5      DBMS_OUTPUT.PUT_LINE('Welcome to ' || S);
  6      -- S := 'Google.com'; -- Not allowed
  7    END;
  8  BEGIN          
  9    WELCOME_PRINT('MySpace.com');
 10    WELCOME_PRINT(SITE);
 11  END;            
 12  /

SQL> EXECUTE WELCOME;
Welcome to MySpace.com
Welcome to FYICenter.com