SQL & PL/SQL

I am trying to accept a user input name string through a PL/SQL substitution variable. I am trying to get the input string to conform to the following format:

FIRST_NAME LAST_NAME TITLE

This is a portion of my code:

ACCEPT strname PROMPT 'Please enter your first name, last name, and title:'

DECLARE
str_name VARCHAR2(100) := '&strname';

I am also trying to generate an exception if any of the three components of the input strings are missing.

I tried using the TO_CHAR function with a format mask. This does not work.

Does anyone have other ideas??

Thanks,