What does the question mark in "Decimal?" mean? [duplicate]

Question

I am following tutorials about MVC4 asp.net. The tutorials are using Decimal like this:

     public Decimal x{ set; get; }
     public Decimal? y{ set; get; }

what does it mean when using ? after Decimal

Answer 1

It means that the value type in question is a nullable type

see here

What is the purpose of a question mark after a type (for example: int? myVariable)?