Variables and operations

One Variable

1. variables are the names of some specific units in the program's memory.

 

2. keyword list:

Auto	Break	Case
Char	Const	Continue
Default	Do	Double
Else	Enum	Extern
Float	For	Goto
If	Int	Long
Register	Return	Short
Signed	Sizeof	Static
Struct	Switch	Typedef
Union	Unsigned	Void
Volatile	While

 

3. Variable type

Type	Storage Unit (in C compiler)				Range
	Bytes	Bits
		Symbol bit	Data bit
Int	4	1	31		-32,768 ~ 32767
Char	1	1	7		-128 ~ 127
Float	4	1	8-digit Index	23-digit ending number	-3.4e-38 ~ 3.4e + 38
Double	8	1	11-digit Index	52-digit ending number	-1.7e-308 ~ 1.7e + 308

 

Register Type: Let the compiler store variables in registers (resident in the CPU itself). The speed of the compiler to access this value is greatly improved, so the program runs faster.

Usage: register type name variable name;

Register Type identifiers should be used for frequently accessed variables to improve program performance.

 

You can use the typedef statement to create your own type: typedef system type name custom type name;

 

4. Assign the octal value or hexadecimal value:

Octal: starts with "0", for example, int octal_value = 0627;

Hexadecimal: starts with "0x", for example, int hex_value = 0xff0;

 

5. escape characters

Escape characters are a special form of characters in C. Generally, escape characters are used to indicate non-printable control characters in the ASCII character set and special function characters. For example, a single marker (') is used to represent a character constant ('), it is used to represent the double apostrophes (") and backslash (/) of string constants. Escape characters are represented by a backslash (/) followed by a character or an octal or hexadecimal number.

Escape Character meaning ASCII code value (decimal)
/A bell (BEL) 007
/B backspace (BS) 008
/F form feed (FF) 012
/N line feed (LF) 010
/R press enter (CR) 013
/T horizontal tabulation (HT) 009
/V vertical tabulation (VT) 011
// Backslash 092
/? Question mark character 063
/'Single quotes character 039
/"Double quotation mark character 034
/0 null character (null) 000
/DDD any character three octal characters
/Xhh any character two hexadecimal

 

6. format the output.

(1). d output a decimal integer
A. % d:
B. % MD: Specify the output width. The number of data digits is smaller than m, left side fill space; greater than m, output by actual number of digits.
A = 123; B = 12345;
Printf ("% 4D, % 4D", a, B );
Output result: _ 123,12345
C. % ld: Output long integer data.
Long A = 123456;
Printf ("% lD", a); % d, error.
Printf ("% 9ld", a); output: ___ 123456

D. % 0ld: 0 fill integer output (replace the space above with 0)
(2). O output Octal numbers
(3). x outputs The hexadecimal number.
(4). U output unsigned data
(5). c Outputs a character
(6). S outputs a string
A. % s printf ("% s". "How ");
B. % Ms
C. %-MS
D. % m. NS
E. %-M. NS
(7). F outputs real numbers in decimal form
A. % F
B. % m. NF
C. %-M. NF
(8). E outputs real numbers in exponential form
A. % E
B. % m. ne
C. %-M. ne

(9) printf uses the right-aligned output by default. If you need the left-aligned output, place a minus sign (-) after %.

 

7. When a local variable with the same name as the global variable is used, the original local variable attributes remain unchanged. This local variable with the same name will temporarily block this global variable.

 

Binary Calculation

1. Operator table

Operators are arranged from top to bottom according to their priority values. operators in the same row have the same priority. The second line is all unary operators.
 

Operator	Explanation	Combination Method
() []->.	Parentheses (functions, etc.), arrays, two types of structure member access	From left to right
! ~ ++ -- +- * & (Type) sizeof	Negative, bitwise negative, incremental, reduced, positive and negative, Indirect, address fetch, type conversion, and Size Estimation	From right to left
*/%	Multiplication, division, modulo	From left to right
+-	Add, subtract	From left to right
<>	Left shift, right shift	From left to right
<<=>=>	Less than, less than or equal to, greater than or equal to, greater	From left to right
=! =	Equal to, not equal	From left to right
&	Bitwise AND	From left to right
^	Bitwise OR	From left to right
|	By bit or	From left to right
&&	Logic and	From left to right
|	Logic or	From left to right
? :	Condition	From right to left
= + =-= * =/= <=>>=	Various assignments	From right to left
,	Comma (Order)	From left to right

 

Auto-increment and auto-increment:It remains unchanged after the change!

 

Bitwise operation:

(1) Displacement Operator

>>: This operation is called the bitwise right shift operator. It shifts the binary number on the left to the specified number of digits on the right.

<: This operation is called the bitwise left shift operator. It shifts the binary value of the number on the left to the specified number of digits on the left.

The displacement operator acts on the variables on the left. The value of the expression on the right is the number of digits to be moved, and the calculation result is the result of the variable to be moved.

For example:

B = A <3. The value of a shifts three places to B, but the value of A does not change.

Shift left to fill 0 in the low position, and shift right to fill 0 in the high position. When the right shift is performed, the result symbol bit can be maintained, that is, when the right shift is performed, if the highest bit is 1, it is a sign bit, then 1 is supplemented instead of 0.

The right-shift operator is often used for integer division, and the left-shift operator is used for integer multiplication. The factor used for multiplication and division must be the power of 2.

 

(2) bitwise logical operators

&: It is called bitwise AND operator. If both bits are 1, the result is 1. Otherwise, the result is 0.

# Include <stdio. h> <br/> void main () <br/> {<br/> printf ("0 & 0 is % d/N", 0 & 0 ); <br/> printf ("0 & 1 is % d/N", 0 & 1); <br/> printf ("1 & 1 is % d/N ", 1 & 1); <br/> printf ("1 & 2 is % d/N", 1 & 2 ); <br/> printf ("15 & 127 is % d/N", 15 & 127); <br/>}

 

Output result:

0 & 0 is 0

0 & 1 is 0

1 & 1 is 1

1 & 2 is 0

15 & 127 is 15

 

 

|: It is called a bitwise OR operator. If one of them is 1, the result is 1. Otherwise, it is 0.

# Include <stdio. h> <br/> void main () <br/> {<br/> printf ("0 | 0 is % d/N", 0 | 0 ); <br/> printf ("0 | 1 is % d/N", 0 | 1); <br/> printf ("1 | 1 is % d/N ", 1 | 1); <br/> printf ("1 | 2 is % d/N", 1 | 2 ); <br/> printf ("128 | 127 is % d/N", 128 | 127); <br/>}

 

Output result:

0 | 0 is 0

0 | 1 is 1

1 | 1 is 1

1 | 2 is 3

128 | 127 is 255

 

^: Bitwise XOR or operator. If two bits are not the same, the result is 1. Otherwise, the result is 0.

# Include <stdio. h> <br/> void main () <br/> {<br/> printf ("0 ^ 0 is % d/N", 0 ^ 0 ); <br/> printf ("0 ^ 1 is % d/N", 0 ^ 1); <br/> printf ("1 ^ 1 is % d/N ", 1 ^ 1); <br/> printf ("1 ^ 2 is % d/N", 1 ^ 2 ); <br/> printf ("15 ^ 127 is % d/N", 15 ^ 127); <br/>}

 

Output result:

0 ^ 0 is 0

0 ^ 1 is 0

1 ^ 1 is 1

1 ^ 2 is 3

15 ^ 127 is 112

 

~ : Bitwise Inverse Operator. This is a single object operator. If it is 1, the result is 0. If it is 0, the result is 1.

 

Length (sizeof) Operator: returns the number of bytes required for a variable or type.