Value Types

Value Types - (Built-in, User defined, Enumerations)

    Value types are on the stack. When copied, the entire value is copied onto the stack again, so doubling the space used on the stack.

Built-in Types

(see table below) (All built in numeric types are 'value' types.)

Numeric Built-in types:

Type	Alias(C#)	Bytes	Range
System.SByte	sbyte	1	-128-127
System.Byte	byte	1	0-255
System.Int16	short	2	-32,768 - 32767
System.Int32	int	4	-2147483648 - 2147483647
System.UInt32	uint	4	0 - 4294967295
System.Int64	long	8	-9223372036854775808 - 9223372036854775807
System.Single	float	8	-3.402823E+38 - 3.402823E+38
System.Double	double	8	-1.79769313486232E+308 - 1.79769313486232E+308
System.Decimal	decimal	16	-79228162514264337593543950335 - 79228162514264337593543950335

*The runtime is optimized for the 32 bit int types so use them when possible.
*The runtime is optimized for 'double' so use it for floating point operations when possible.

Other Built-in value types (non numeric)

Type	Alias(C#)	Bytes	Range
System.Char	char	2	single unicode characters
System.Boolean	bool	4	True/False
System.IntPtr	(none)	Platform dependent	Pointer to mem address
System.DateTime	date	8	1/1/0001 12:00:00 AM to 12/31/9999 11:59:59 PM

There are 300 more value types in the Framework, but above are the most common.

User-defined Types

Structs - Similar to class but stored on the stack.
Structs should:

1. Logically represent a single value
2. Has an instace size less than 16 bytes
3. Will not be changed after creation
4. Will not be caset to reference type

You can convert a struct to a class by changing the keyword 'struct' to 'class', and then it will be allocated on the managed heap instead of the stack. Structs generally perform better than classes if the size is 16 bytes or less.

Enumerations

// C#
enum Titles: int {Mr, Ms, Mrs, Dr};

represents a list for the developer to choose from.
-simplify code readability
-provides safety when users need to choose from specific values.
 

 

More on Value types:

 You don't use the 'new' keyword when creating an instance (int i = 0;)
 Best to assign a value when constructing, but not required.
 
 

New in .Net 2.0 - Nullable types

 Nullable<int> i = null;
 or
  int? i = null;

 With nullable types, you can use the 'HasValue' property to see if its null or not
 if(i.HasValue)
  //do something