[embedded C foundation] Part 3: constants and variables

1 Constant

Constant : It is not allowed to change the quantity into a constant

1.1 Integer constant

Decimal constant 100
Octal constant 0100（ Octal constants are expressed in 0 start ）
Hexadecimal constant 0x100
100L 100l Long integer 100
100UL 100ul Unsigned long 100

int a = 100L;（long int Type is also 4 byte ）

1.2 Floating point constants

3.1415
3.1415e15（ namely 3.1415 multiply 10 Of 15 Power ）
3.1415e-15
3.1415E15
3.1415E-15

1.3 character constants

‘a’
‘A’
’ ’ Space character
‘\0’ \0 character
‘\n’ A newline
‘\t’ Horizontal tabs
‘\r’ enter
‘\b’ backspace operator
‘\v’ Vertical tabs
‘\a’ Ring the bell
‘\’ \ Symbol
‘’’ ' Symbol
‘"’ " Symbol

 Escape character
C In language , A character can be used in addition to its entity （ That is, the real character ） Express , It can also be represented by coded values . This way of using encoded values to indirectly represent characters is called escape characters （Escape Character）.

Escape characters to \ perhaps \x start , With \ The beginning represents the encoded value followed by octal form , With \x The beginning represents the encoded value followed by hexadecimal form . For escape characters , Only octal or hexadecimal can be used .

character 1、2、3、a、b、c Corresponding ASCII The octal forms of the codes are 61、62、63、141、