To extend on the topic of user input validations, The member's ID number is used in several area's through out the entire
The validation method for a this value is stored in the Business Layer (tier) and is called to from the Presentation
Layer (our form in this case). This type of a modular (plug and use) design allows any application to validate this value
regardless of what it was or where it was.
For instance, a web client could just as easily validate their MemberID number as the Windows Form did or another process
And since all other processes in and using the application use it to validate, if the business rules for validating the
MemberID value changed, There would only be one easy to find place in the code to make that change. Next is a second example
of user input validation from the Library Management Application's Business Tier.
In this example the format and data type for the Zip Code Value is checked for 2 different possible formats with the
C# Regex (regular expressions) class and a set of nested IF statements to determine its validity.