(ii) predefined data types

I. Value types and reference types

1. Difference between a value type and a reference type

(1) Value types store values directly, reference types are stored on worthy references

(2) value types are stored on the stack, and reference types are stored on the managed heap

2, if the variable is a reference, you can set its value to NULL, indicating that it does not reference any object

3. In C #, basic types such as bool and long are value types. Instead, most of the more complex C # data types, including the classes we declare ourselves, are reference types.

4. If you need to define your type as a value type, you should declare it as a struct.

Two. CTS type

The basic predefined types that C # recognizes are not built into the C # language, but are embedded within the. NET Framework.

Three. Pre-defined value types

1. Integral type

Name	CTS Type	Description	Range
SByte	System.SByte	8-bit signed integer	-128~127 (-2 of 8-Time Square-7-1)
Short	System.Int16	16-bit signed integer	-32768~32767 (-2 of 15-time Square-15-1)
Int	System.Int32	32-bit signed integer	-2417483648~2147483647 (-2 of 31-Time Square-31-1)
Long	System.Int64	64-bit signed integer	-9223372036854775808~9223372036854775807 (-2 of 63-time Square-63-1)
Byte	System.Byte	8-bit unsigned integer	0~255 (0~2 8-1)
UShort	System.UInt16	16-bit unsigned integer	0~65535 (0~2 16-1)
UInt	System.UInt32	32-bit unsigned integer	0-4294967295 (0~2 32-square-1)
ULong	System.UInt64	64-bit unsigned integer	0~18446744073709551615 (0~2 64-1)

Variables of all integer types can be assigned decimal or hexadecimal values, which require a 0x prefix.

1long x=0x12ab

2. Floating-point types

Name	CTS Type	Description	Number of digits	Range (approximate)
Float	System.Single	32-bit single-precision floating-point number	7	+-1.5 x 10 of 245 square ~+-3.4 x 10 38-Time Square
Doble	System.Double	64-bit double-precision floating-point number	15/16	+-5.0 x 10-324 Square ~+-1.7 x 10 308-Time Square

3.decimal type

Name	CTS Type	Description	Number of digits	Range (approximate)
Decimal	System.Decimal	128-bit high-precision decimal number notation	28	+-1.0 x 10-28 Square ~+-7.9 x 10 28-Time Square

4.bool type

Name	CTS Type	Description	Number of digits	Value
bool	System.Boolean	Indicates true or FALSE	NA	Teue or False

5. Character types

Name	CTS Type	Value
Char	System.Char	Represents a 16-bit Unicode character

The literal of a char type is enclosed in single quotation marks, such as ' A '. If you put the character in double quotes, the compiler will treat it as a string, resulting in an error.

Common escape characters

Escape sequences	Character
\‘	Single quotation marks
\"	Double quotes
\\	Back slash
/	Empty
\a	Warning
\b	Backspace
\f	Page change
\ n	Line break
\ r	Enter
\ t	Horizontal tab
\v	Vertical tab

6 pre-defined reference types

Name	CTS Type	Description
Object	System.Object	Root type, other types in the CTS are derived from it (including value types)
String	System.String	Unicode string

(ii) predefined data types