Lession 07: Data types in C#

In the previous section, we have seen that a variable must be declared with the data type because C# is a strongly-typed language. For example,

string message = "Hello World!!";

string is a data type, message is a variable, and "Hello World!!" is a string value assigned to a variable - message.

The data type tells a C# compiler what kind of value a variable can hold. C# includes many in-built data types for different kinds of data, e.g., String, number, float, decimal, etc.

Example: Data types

class Program
{
    static void Main(string[] args)
    {
        string stringVar = "Hello World!!";
        int intVar = 100;
        float floatVar = 10.2f;
        char charVar = 'A';
        bool boolVar = true;

    }
}

Each data types includes specific range of values. For example, a variable of int data type can have any value between -2,147,483,648 to 2,147,483,647. The same way, bool data type can have only two value - true or false. The following table lists the data types available in C# along with the range of values possible for each data type:

Alias	.NET Type	Type	Size (bits)	Range (values)
byte	Byte	Unsigned integer	8	0 to 255
sbyte	SByte	Signed integer	8	-128 to 127
int	Int32	Signed integer	32	-2,147,483,648 to 2,147,483,647
uint	UInt32	Unsigned integer	32	0 to 4294967295
short	Int16	Signed integer	16	-32,768 to 32,767
ushort	UInt16	Unsigned integer	16	0 to 65,535
long	Int64	Signed integer	64	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
ulong	UInt64	Unsigned integer	64	0 to 18,446,744,073,709,551,615
float	Single	Single-precision floating point type	32	-3.402823e38 to 3.402823e38
double	Double	Double-precision floating point type	64	-1.79769313486232e308 to 1.79769313486232e308
char	Char	A single Unicode character	16	Unicode symbols used in text
bool	Boolean	Logical Boolean type	8	True or False
object	Object	Base type of all other types
string	String	A sequence of characters
decimal	Decimal	Precise fractional or integral type that can represent decimal numbers with 29 significant digits	128	(+ or -)1.0 x 10e-28 to 7.9 x 10e28
DateTime	DateTime	Represents date and time		0:00:00am 1/1/01 to 11:59:59pm 12/31/9999

As you can see in the above table that each data types (except string and object) includes value range. Compiler will give an error if value goes out of datatype's permitted range. For example, int data type's range is -2,147,483,648 to 2,147,483,647. So if you assign value which is not in this range then compiler would give error.

Example: Compile time error

// compile time error: Cannot implicitly convert type 'long' to 'int'.
int i = 21474836470; 

Alias vs .Net Type:

In the above table of data types, first column is for data type alias and second column is actual .Net type name. For example, int is an alias (or short name) for Int32. Int32 is a structure defined in System namespace. The same way, string represent String class.

Alias	Type Name	.Net Type
byte	System.Byte	struct
sbyte	System.SByte	struct
int	System.Int32	struct
uint	System.UInt32	struct
short	System.Int16	struct
ushort	System.UInt16	struct
long	System.Int64	struct
ulong	System.UInt64	struct
float	System.Single	struct
double	System.Double	struct
char	System.Char	struct
bool	System.Boolean	struct
object	System.Object	Class
string	System.String	Class
decimal	System.Decimal	struct
DateTime	System.DateTime	struct

Data types are further classified as value type or reference type, depending on whether a variable of a particular type stores its own data or a pointer to the data in the memory.

Learn about variables in value type and reference type in the next section.