SQL & PL/SQL :: Using NVL Function With Parameters In A Procedure?

I am currently studying a Foundation degree in computer software development, and one of my assignment in PL/SQL I am stuck on one of the tasks.

I have to create a procedure where one of the parameters needs to have a default value of one, if no value is entered when the procedure is called. I have trued to use the NVL function which worked when using a anonymous block, but now I have to convert that to a procedure. My problem is I'm getting an error.

The code for the procedure is

CREATE OR REPLACE PROCEDURE add_new_classes
(p_number_of_classes NUMBER := NVL(NULL,1), -- This will enter a default value of 1 if the user does not specify a number
p_course_id classes.course_id%TYPE,
p_period classes.period%TYPE,
p_frequency classes.frequency%TYPE,

[code]....

I then use this to test it

BEGIN
add_new_classes(1002,'first','daily',3002);
END;

and the error I get is

Quote:ORA-06550: line 2, column 4:
PLS-00306: wrong number or types of arguments in call to 'ADD_NEW_CLASSES'
ORA-06550: line 2, column 4:
PL/SQL: Statement ignored
1. BEGIN
2. add_new_classes(1002,'first','daily',3002);
3. END;