Type and Storage

What is The Type?

A type defines the blueprint for a value, in the other way we can say that type is a template for creating data structures.It isn’t the data structure itself, but it specifies the characteristics of objects constructed from the template.

A type is defined by the following elements:

• A name
• A data structure to contain its data members
• Behaviors and constraints

Image above show us the structure of int and short.

Data Members and Function Members

There are two kinds of members in a type: data members and function members.

• Data members store data that is relevant to the object of the class or to the class as a whole.
• Function members execute code. Function members define how the type can act.

Figure below shows you int member:

Type Classification

A type can be classified based on how they defined and how they are stored in memory. From the way a type defined, we can separate to two groups, pre-defined and user-defined type. From how a type stored in memory, we can separate them in to value type and reference type.

Predifined Types	simple	Non-Numeric	bool
			char
		Numeric	Integer	8-Bit	sbyte
					byte
				16-Bit	short
					ushort
				32-Bit	int
					uint
				64-Bit	long
					ulong
			Floating Point	decimal
				float
				double
	object
	string
	Dynamic
Userdefined Types	class Type
	struct types
	array types
	enum types
	delegate types
	interface types

Predifined Types

Table below show Simple Predifined Type

Name	Meaning	Range	.NET Framework Type	Default Value
sbyte	8-bit signed integer	-128 – 127	System.SByte	0
byte	8-bit unsigned integer	0 – 255	System.Byte	0
short	16-bit signed integer	-32,768 – 32,767	System.Int16	0
ushort	16-bit unsigned integer	0 – 65,535	System.UInt16	0
int	32-bit signed integer	-2,147,483,648 – 2,147,483,647	System.Int32	0
uint	32-bit unsigned integer	0 – 4,294,967,295	System.UInt32	0
long	64-bit signed integer	-9,223,372,036,854,775,808 – 9,223,372,036,854,775,807	System.Int64	0
ulong	64-bit unsigned integer	0 – 18,446,744,073,709,551,615	System.UInt64	0
float	Single-precision float	1.5×10-45–3.4×1038	System.Single	0.0f
double	Double-precision float	5×10-324–1.7×10308	System.Double	0.0d
decimal	Decimal value with 28-significant-digit precision	±1.0×1028–±7.9×1028	System.Decimal	0m
bool	Boolean	true, false	System.Boolean	false
char	Unicode character	U+0000–U+ffff	System.Char	\x0000
char	Unicode character	U+0000–U+ffff	System.Char	\x0000

Table below show Non-Simple Predifined Type

Name	Meaning	.NET Framework Type
object	The base class from which all other types, including the simple types are derived	System.Object
string	A sequence of zero or more Unicode characters	System.String
dynamic	A type designed to be used with assemblies written in dynamic languages	No corresponding .NET type

Userdefined Types

Besides predifined types, we can also create our own-defined class. C# provides six kinds of custom defined class, as below:

• class types
• struct types
• array types
• enum types
• delegate types
• interface types

Different from predifined types, userdefined type you need to create a type declaration, which includes the following information:

• The kind of type you are creating
• The name of the new type
• A declaration (name and specification) of each of the type’s members—except for array and delegate types, which don’t have named members

For example, figure below shows you how to work with user defined class.

Value Type and Reference Type

Stack and Heap

Stack is a list of memory that acts as a last-in, first-out (LIFO) data structure. It stores several types of data:

• The values of certain types of variables
• The program’s current execution environment
• Parameters passed to methods

Heap is an area of memory where chunks are allocated to store certain kinds of data objects. Unlike the stack, data can be stored and removed from the heap in any order.
Although you can store data in heap, but you can't delete them explicitly. Instead, the Garbage Collector (GC) will do it for you. When your program doesn't access the object in memory, the GC will delete and free the memory. This will free us from memory leaking problem.

Value Types and Reference Types

Types are divided into two categories: value types and reference types. Objects of these types are stored differently in memory.

• Value types require only a single segment of memory, which stores the actual data.
• Reference types require two segments of memory:
  • The first contains the actual data—and is always located in the heap.
  • The second is a reference that points to where the data is stored in the heap.

Category		Description
Value types	Simple types	Signed integral: sbyte, short, int, long
		Unsigned integral: byte, ushort, uint, ulong
		Unicode characters: char
		IEEE flating point: float, double
		High-precision decimal: decimal
		Boolean: bool
	Enum types	User-defied types of the form enum E {...}
	Struct types	User-defied types of the form struct S {...}
	Nullable types	Nullable types Extensions of all other value types with a null value
Reference types	Class types	Ultimate base class of all other types: object
		Unicode strings: string
		User-defied types of the form class C {...}
	Interface types	User-defied types of the form interface I {...}
	Array types	Single- and multi-dimensional; for example, int[] and int[,]
	Delegate types	User-defied types of the form e.g. delegate int D(...)

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