Value Types

Value types are derieved from two main categories Structs & Enumerations.
Structs fall into the following categories
  - Integral types
  - Floating-point types
  - decimal
  - bool
  - User defined structs

Value types are contained on the stack , assigning one value type variable to another copies the
contained value.  This differs from reference types, which are stored on the managed heap and
copying a reference type copies the reference to the object but not the object itself.

Console.WriteLine("a = {0}", a);
Console.WriteLine("b = {0}", b);

a = b;
b = 4;
   
Console.WriteLine("a = {0}", a);
Console.WriteLine("b = {0}", b);


       
The variable a starts off with a value of 1 and b with a value of 2.
The contents of variable b are copied to a and variable b set to 4.
However changing variable b does not affect variable a, which has
a copy of the contents of variable b.

All value types are derieved from System.ValueType one interesting type is System.String this doesn't derieve from System.ValueType  but acts like a value type, it is immutable a new instance is created
each time it is changed unlike other reference types.

string a = "first string";
string b = "second string";
Console.WriteLine("string a = {0}", a);
Console.WriteLine("string b = {0}", b);
      
b = a;
a = "modified string a";
Console.WriteLine("string a = {0}", a);
Console.WriteLine("string b = {0}", b);

Unlike reference types, it is not possible to derieve a new type from a value type.  However, like reference types, structs can implement interfaces.