Change IN parameter in Procedure

What will happen if you you change the IN parameter in a Procedure? with detailed explanation?

What do you mean by change the IN parameter ?

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.


If you try to change in parameter value inside a procedure it will through error message
expression 'XX' cannot be used as an assignment target