1how to type the code for a log in function?
descriptions: to enable librarian to log in. all the username and password of the librarian of the librarian is store in file called ''librarian_id.txt''.
*the code must include printf invalid format if user input invalid format.
*my learnt topic is ...function, making decision, repetition, text input/output, arrays and strings.
*the code should use this few topics only and not go to far.