(How)
C^# You Are - 10 December 2006

1. What does the ?: operator do in C#?  Answer
   The ?: operator is equivalent to an if-else statement except the result is an expression.  It has the syntax:
   
      cond ? a : b
   
   If cond evaluates to true then a is returned.  Otherwise b is returned.  a and b must be of the same type.  This operator is useful in expressions such as assignment expressions.
   
      string newValue = (value != null) ? value.Trim() : "";
     
2. What does the ?? operator do in C#?  Answer
   This operator was added to C# 2.0. It is similar to the ?: operator in that it evaluates a condition and returns one of two values.  The syntax is:
   
      reference ?? a 
   
   If reference is null then it returns a otherwise it returns reference. 
   
      string newValue = value ?? "";
   
3. What does the as operator do in C#?  Answer
   The as operator is a typecast operator in C#.  The syntax is:
   
      value as type
   
   If value is of the given type or can be converted to the type then value is returned as that type.  Otherwise null is returned.  This is the preferred manner in which to do runtime type checking.
   
       public void Foo ( object value )
       {
          IMyInterface ifc = value as IMyInterface;
          if (ifc != null)
          {
          };
       }
   
4. What does the is operator do in C#?  Answer
   The is operator is a type checking operator.  The syntax is:
   
      value is type
   
   The operator returns true if value is of the given type or can be converted to the type or false otherwise.  This operator is good for conditional checking but you should use as if you are going to do something with the value.
   
      if (value is typeof(string))
      {
       }
   
5. What does CTS stand for in .NET?  Answer
   CTS stands for Common Type System. The CTS provides a common set of types for use in all .NET languages.  All .NET languages support the given type although most languages will provide alternative names for the types.  The CTS is part of what makes compatibility across languages possible.
   
6. What does CLS stand for in .NET?  Answer
   CLS stands for Common Language Specification. The CLS identifies the common features that all .NET languages need to support.  If an assembly, type, type member or other .NET feature is marked as CLS compliant then any .NET language can use the feature.  It is important to try to make all types and type members CLS compliant whenever possible.
   
7. For each of the following types, are they CLS compliant?  Answer
   1. Byte
   2. UInt16
   3. Int32
   4. Double
   5. String
   6. Decimal
   7. UInt64
   8. Boolean
   1. Yes
   2. No
   3. Yes
   4. Yes
   5. Yes
   6. Yes
   7. No
   8. Yes

8. What is a nullable type (in terms of v2 and not in regard to reference types)?  Answer
   A nullable type is a value type that can either hold a null value or a value type value.  Nullable types were added in v2 in order to support better integration with databases where column values can be null.  In reality a nullable type is simply a structure with space for the value type value and a flag indicating if the value is null.
   
   (Updated 28 Dec 2006 w/ comments received from James Curran)
   
9. What is the difference between a reference type and a value type?  Answer
   A type that is represented as a pointer (or referenced) to the actual data in .NET.  Two or more objects that are assigned to the same reference type object represent the same object.  Any changes to the first object also change the second object.  In .NET reference types include classes, interfaces, strings and delegates.
   
   A value type is any type that is not a reference type.  A value type represents a block of memory.  Each variable of a value type represents a distinct copy of the type.  A change in one copy does not impact the other.  Value types have serious limitations in .NET.  In .NET value types include structures, enumerations and all primitive types
   
10. Is string a reference or value type?  Answer
    It is a reference type although it exhibits value semantics.  Assigning a string variable to another string variable effectively creates a copy.  In reality whenever a string value is changed a new copy of the string is created in memory.  This is known as being immutable.