When would a required field validation be used in an

3.1 when would a required field validation be used in an application? In
your example, what error message would you give if the validation
failed?
3.2 when would a Data Type validation be used in an application? In
your example, what error message would you give if the validation
failed?

ModelState.AddModelError(“Date”,”please enter a date”)
3.3 when would a regular expression validation be used in an
application? In your example, what error message would you give if the
validation failed?
4.1 what is the difference between String and string data types in
ASP.NET MVC applications.
The string in ASP.NET MVC is just an alias for System.String. Generally, where the string is, you can
also use the String as an alternation. However, that doesn’t means there is nothing to say about
the difference between String and string:
1. ”string” is a reserved keyword in C#, “String” is not, that means you can use String as a
variable name but not “string”.
2. Only when there’s no such a class interface,struct, emun etc which named as “String”
and the “System” namespace has been imported by “using System.String”, the String can
be treated as “System.String”.

4.2why do String/string data types play an important role in web
applications that use the HTTP/HTTPS protocol?(not sure for this issue)