Data Types in C sharp

Data Types in a programming language describes that what type of data a variable can hold . C# is a strongly typed language, hence you have to define data type for variables. you cannot use variable without data types.

When we declare a variable, we have to tell the compiler about what type of the data the variable can hold or which data type the variable belongs to.

  Syntax : DataType VariableName                                 

  DataType : The type of data that the variable can hold

  VariableName : the variable we declare for hold the values.

The varibles in C#, are categorized into the following types:

• Value types
• Reference types
• Pointer types

Value Types:

 If a variable holds actual value then the type of data types are value types. Value type variables can be assigned a value directly. They are derived from the class System.ValueType. These value types are stored in “stack” memory and these value types are fixed in size. If you assign a value of a variable to another variable it will create two copies.

Ex: byte, short, int, float, double, long ,char, bool, DateTime.

All primitive data type except string and object are example of value types.

Object is a super type. It can store any type and any size of data. Object is called super type because it helps in inheritance.

struct and enum are value type.

CSharp has a set of predefined value types.

Data Type	Description	Nanespace Class	Range
bool	Boolean value	System.Boolean	True or False
byte	8-bit unsigned integer	System.Byte	0 to 255
char	16-bit Unicode character	System.Char	U +0000 to U +ffff
decimal	128-bit precise decimal values with 28-29 significant digits	System.Decimal	(-7.9 x 1028 to 7.9 x 1028) / 100 to 28
double	64-bit double-precision floating point type	System.Double	(+/-)5.0 x 10-324 to (+/-)1.7 x 10308
float	32-bit single-precision floating point type	System.Single	-3.4 x 1038 to + 3.4 x 1038
int	32-bit signed integer type	System.Int32	-2,147,483,648 to 2,147,483,647
long	64-bit signed integer type	System.Int64	-923,372,036,854,775,808 to 9,223,372,036,854,775,807
sbyte	8-bit signed integer type	System.Sbyte	-128 to 127
short	16-bit signed integer type	System.Int16	-32,768 to 32,767
uint	32-bit unsigned integer type	System.UInt32	0 to 4,294,967,295
ulong	64-bit unsigned integer type	System.UInt64	0 to 18,446,744,073,709,551,615
ushort	16-bit unsigned integer type	System.UInt16	0 to 65,535

Reference types

A variable holds  the address of value instead of  actual  value stored in memory . If multiple variables  reffering to a memory location. If the data in the memory location is changed by one of the variables, the other variable automatically reflects this change in value .These reference types are stored in “heap” memory . Reference types are not fixed in size.  They are maintained in system managed heap but it also uses stack to store reference of the heap Two primitive types (string and object) and non-primitive data types (class, interface & delegate) are examples of reference type. Example of  reference types are: object, dynamic, and string.

Object Type

The Object Type is derived from System.Object class. The object types can be assigned values of any other types, value types, reference types, predefined or user-defined types. However, before assigning values, it needs type conversion.

When a value type is converted to object type, it is called boxing and on the other hand, when an object type is converted to a value type, it is called unboxing.

object obj;

obj = 100; // this is boxing

Dynamic Type

We can assign any type of value in the dynamic data type variable. Type checking  of variables takes place at run-time.

Syntax for declaring a dynamic type is:

dynamic <variable_name> = value;

For example,

dynamic d = 100;

Dynamic types are similar to object types but the only difference is that type checking for object type variables takes place at compile time, whereas that for the dynamic type variables takes place at run time.

String Type

The String Type allows you to assign any string values to a variable. The string type is an alias for the System.String class. It is derived from object type. The value for a string type can be assigned using string literals in two forms: quoted and @quoted.

For example,

String str = "Suhail Osmani";

The user-defined reference types are: class, interface, or delegate. We will discuss these types in later chapter.

Pointer Type

Pointer type variables store the memory address of another type. Pointers in C# have the same capabilities as the pointers in C or C++.

Syntax :

type* identifier;

Example,

char* mhb;

int* hjv;