# C # logic operations

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&, ^ ,! And | operators are called logical operators. Operators are used to connect computing objects with C # syntax. Operators are called logical expressions. Logical operator "!" And "^" only act on the subsequent operands, so it is called The unary operator. "&", "|", "&", And "|" are binary operators. These four operators are used for expressions and generate a true or false logical value.

If x is true, y is not calculated (because the result of the "or" operation is true regardless of the value of y ). This is called a "Short Circuit" calculation.

&&

If x is false, y is not calculated (because the "and" operation result is false regardless of the value of y ). This is called a "Short Circuit" calculation.

|

The result is false only when both operands are false.

&

True is returned only when both operands are true.

^

True is returned only when only one operand is true.

~

Operators perform bitwise complement operations on the operands. The result is equivalent to reversing each bit.

Definition

An exclusive or (xor) is a mathematical operator. It is applied to logical operations. The XOR symbol is "^ ". The algorithm is a XOR or B = a' B or AB '(a' Is Not ). True or false results are true, false or true results are true, true or false results are false, and false results are false. That is to say, if two values are different, they are different or the result is true. Otherwise, it is false. The difference is 1, the same is 0, for example, 1001 is different or 1010 is equal to 0011. an exclusive or semi-addition operation is equivalent to a binary addition that does not bring in bits. In a binary system, 1 indicates the truth, 0 indicates false, and then the exclusive or operation is as follows: 0 or 0 = 0, 1, 0 = 1, 0, or 1 = 1, 1, or 1 = 0. These rules are the same as the addition, but do not bring in a bit.

Exclusive or Algorithm

1. a ^ B = B ^ a 2. a ^ B ^ c = a ^ (B ^ c) = (a ^ B) ^ c; 3. d = a ^ B ^ c can release a = d ^ B ^ c. 4. a ^ B ^ a = B. x is the binary number 0101 y is the binary number 1011 then the result is x ^ y = 1110 0 ^ 0 = 0 0 ^ 1 = 1 1 ^ 0 = 1 1 ^ 1 = 0 only in the result of two comparison bits is 1, otherwise, the result is 0, that is, "the same is 0, and the difference is 1 "!

 Input Operator Input Result 1 ^ 0 1 1 ^ 1 0 0 ^ 0 0 0 ^ 1 1
XOR logic

Logical symbols of the XOR logic, suchFigure 2As shown in, the truth table is shown inFigure 1. The logic of XOR is: When AB is not the same, the output P = 1; When AB is the same, the output P = 0. "Operator" is an exclusive OR operator symbol. The logic of an exclusive or logic is also a combination of or non-logic. Its logical expression is:

P = A branch B

0 bytes 0 = 0

0 bytes 1 = 1

1 bytes 0 = 1

1 bytes 1 = 0

Function

It is widely used in computers. The logic symbol ^ (Shift + 6) of an exclusive or (xor) is added to a circle.+(Optional) or·. The image is represented:

True ^ false = true

False ^ true = true

False ^ false = false

True ^ true = false

Or:

True ^ False = True

False ^ True = True

False ^ False = False

True ^ True = False

Some computer languages use 1 to indicate true, and 0 to indicate false. Therefore, the two bytes are bitwise OR the following:

00000000 or 00000000 = 00000000

11111111 or 00000000 = 11111111

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1, Bit logical non-operationBit logical non-operation is a single purpose and only one operation object. Bitwise logical non-operation performs non-operation on the value of the computing object by bitwise. That is, if a bit is equal to 0, it is converted to 1. If a bit is equal to 1, convert it to 0. For example, if the bitwise logic is not performed on Binary 10010001, the result is equal to 01101110, which is represented in decimal :~ 145 is equal to 110; bitwise logic is not performed on Binary 01010101, and the result is equal to 10101010. In decimal format ~ 85 equals 176.

2 Bit logic and OperationBitwise logic and Operations perform and perform operations on two calculation objects by bit. And calculation rules: 1 and 1 are equal to and 0 is equal to 0. For example, 10010001 (Binary) & 11110000 equals 10010000 (Binary ).

3, Bit logic or operationBitwise logic or operation performs or on two operation objects by bit. The rule of the or operation is: 1, 1, or 0 equals 1, 0 or 0 equals 0. For example, 10010001 (Binary) | 11110000 (Binary) equals 11110001 (Binary ).

4 Bitwise logical exclusive or operationBitwise logical exclusive or operation performs bitwise exclusive or operation on Two Computing objects. The rule for an exclusive or operation is: 1 exclusive or 1 equals 0, 0 exclusive or 0 equals 0. That is, 0 is the same, and 1 is different. For example, 10010001 (Binary) ^ 11110000 (Binary) equals 01100001 (Binary ).

5 Bitwise left shift operationThe bitwise left shift operation shifts the entire number to several places by bit, and the portion left after the shift is left is 0. For example, if the eight-bit byte Variable byte a = 0x65 (that is, 01100101 of the binary value), remove it three places to the left: the result of a <3 is 0x27 (00101000 of binary ).

6 Bitwise right shift operationThe bitwise right shift operation shifts the entire number to several places by bit, and the portion left blank after the right shift is set to 0. For example, the eight-bit byte Variable Byte a = 0x65 (both (Binary 01100101) shifts it three places to the right: a> 3 is 0x0c (Binary 00001100 ). When bitwise AND, Or, exclusive or operations are performed, if the types of the two operation objects are the same, the type of the operation result is the type of the operation object. For example, if two int variables a and B are compared, the type of the operation result is still int. If the types of the two calculation objects are inconsistent, C # converts the types of the inconsistent objects to the same type and then performs the operation. The type conversion rules are the same as those for integer conversions in arithmetic operations.

A bitwise operator is a bitwise expression that connects integer values.     (Details 2)

1. bitwise AND operator (&)
1. Operation Rules
For the two data involved in the operation, the "and" operation is performed by binary. If the two corresponding binary values are 1, The result value of this bit is 1; otherwise, it is 0, that is:
0 & 0 = 0 0 & 1 = 0, 1 & 0 = 0, 1 & 1 = 1.
2. Purpose
(1) resetting
Calculation object: the first digit in the original number, and the corresponding digit in the new number is 0.
(2) locate certain indicators in a number.
To take the low (high) byte of an integer a (two bytes), you only need to bitwise the 377 (177400) of a and 8 bytes.
(3) retain a certain digit Of a certain number.
Perform an & operation with a number. This number is 1 in this bit.
3. For example, 9 & 5 can be written as follows: 00001001 (Binary complement of 9) & 00000101 (Binary complement of 5) 00000001 (Binary complement of 1) 9 & 5 = 1.
Bitwise AND operations are usually used to clear some bits or retain some bits. For example, if a clears the high eight bits of 0 and retains the low eight bits, it can be used as a & 255 operation (255 of the binary number is 0000000011111111 ).
Main (){
Int a = 9, B = 5, c;
C = a & B;
Printf ("a = % d \ nb = % d \ nc = % d \ n", a, B, c );
}

2. bitwise OR operator (|)
1. Operation Rules
For the two data involved in the operation, the "or" operation is performed by binary. If both of the two data are 0, the result value of this bit is 0; otherwise, it is 1, that is:
0 | 0 = | 1 = | 0 = | 1 = 1.
2. Purpose
Some bits of a data are set to 1.
3. Example: 9 | 5: 00001001 | 00000101
00001101 (decimal 13) Visible 9 | 5 = 13
Main (){
Int a = 9, B = 5, c;
C = a | B;
Printf ("a = % d \ nb = % d \ nc = % d \ n", a, B, c );
}

3. XOR operator (^)
It is also called the XOR operator.
1. Operation Rules
If the two binary carry numbers involved in the calculation are the same, the result is 0 (false); the difference is 1 (true), that is:
0 ^ 0 = 0 0 ^ 1 = 1 1 ^ 0 = 1 1 ^ 1 = 0.
2. Purpose
(1) enable specific positioning to flip
If there is 01111010, and you want to lower it by 4 bits, you can perform the ^ operation with 00001111.
(2) equal to 0 ^, retain the original value
(3) exchange two values without temporary variables
Suppose a = 3, B = 4. To swap values of a and B, use the following value assignment statement:
A = a ^ B; B = B ^ a; a = a ^ B;
3. For example, 9 ^ 5 can be written as follows: 00001001 ^ 00000101 00001100 (12 in decimal format)
Main (){
Int a = 9;
A = a ^ 15;
Printf ("a = % d \ n", );
}

4. Inverse operators (~)
1. Operation Rules
~ It is a single object (Meta) operator used to reverse a binary number by bit, that is, to change 0 to 1, 1, and to 0.
2. Purpose
To set the percentile of an integer a to 0, use a = &~ 1;
3. For example ~ 9 is calculated as follows :~ (0000000000001001) Result: 1111111111110110

5. Left shift operator (<)
1. Operation Rules
This parameter is used to remove all binary numbers of a number from the left, and add 0 to the right, overflow after the high left shift, and discard does not work.
2. Purpose
Shifts one digit to the left, which is multiplied by 2.
3. For example, if a = 15, a> 2, 000001111 is shifted to 00000011 (decimal 3 ). It should be noted that, for the number of signed characters, the symbol bit will be moved along with the right shift. When it is a positive number, the maximum bit is 0, while the negative number, the sign bit is 1, the maximum bit is 0 or fill 1 depends on the provisions of the compilation system. Turbo C and many systems require completing 1.
Main (){
Unsigned a, B;
Printf ("input a number :");
Scanf ("% d", & );
B = a> 5;
B = B & 15;
Printf ("a = % d \ tb = % d \ n", a, B );
}
Let's look at another example!
Main (){
Char a = 'A', B = 'B ';
Int p, c, d;
P =;
P = (p <8) | B;
D = p & 0xff;
C = (p & 0xff00)> 8;
Printf ("a = % d \ nb = % d \ nc = % d \ nd = % d \ n", a, B, c, d );
}

6. Right Shift Operator (>)
1. Operation Rules
It is used to shift all the binary numbers of a number to several places on the right, and the low position to the right is discarded. For the unsigned number, the high position is supplemented with 0;
For the number of symbols, move the left to 0 ("logical right shift") or 1 ("arithmetic right shift ")
2. Purpose
Shifts one digit to the right is equal to dividing by 2

VII. bitwise assignment operators
Bitwise operators and value assignment operators can form a composite value assignment operator, for example:
<=, |=, >=, <=, ^ =

8. bitwise operations for data of different lengths
If the two data lengths are different, when bitwise operations (for example, a & B, while a is long and B is int) are performed, the system will align the two to the right. If B is a positive number, the left 16 digits are filled with 0. If B is a negative number, the left end is filled with 1. If B is an unsigned integer, the left end is filled with 0.

Bit domain

When storing some information, it does not need to occupy a full byte, but only needs to occupy a few or one binary bit. For example, when storing a switch value, there are only two States: 0 and 1. Use one binary digit. To save storage space and simplify processing, the C language also provides a data structure called "bit domain" or "bit segment ". The so-called "bit field" refers to dividing the binary character in a byte into several different regions and showing the digits of each region. Each domain has a domain name, which allows operations by domain name in the program. In this way, several different objects can be represented by a byte binary field. 1. Definition of a bit field and description of a bit field variable the definition of a bit field is similar to that of a structure, in the form:
Struct bit domain structure name
{Bit domain list };
The format of the bit domain list is: type description Character Domain Name: Bit domain Length

For example:
Struct bs
{
Int a: 8;
Int B: 2;
Int c: 6;
};
The description of bitfield variables is the same as that of structure variables. You can first define and then describe, and define or directly describe these three methods. For example:
Struct bs
{
Int a: 8;
Int B: 2;
Int c: 6;
} Data;
It indicates that data is a bs variable, which occupies two bytes in total. Where a occupies 8 places, B occupies 2 places, and c occupies 6 places. The definitions of bit domains are described as follows:

1. A single-byte field must be stored in the same byte, and cannot span two bytes. If the remaining space of one byte is insufficient to store another domain, it should be stored from the next unit. You can also intentionally start a domain from the next unit. For example:
Struct bs
{
Unsigned a: 4
Unsigned: 0/* airspace */
Unsigned B: 4/* stored from the next unit */
Unsigned c: 4
}
In the definition of this bit field, a occupies 4 bits in the first byte, And the last 4 bits enter 0 to indicate that it is not used. B starts from the second byte and occupies 4 bits, and c occupies 4 bits.

2. Because the bit field cannot span two bytes, the length of the bit field cannot exceed the length of one byte, that is, it cannot exceed 8-bit binary.

3. A bit domain can be a non-bit domain name. In this case, it is only used for filling or adjusting the position. An anonymous domain cannot be used. For example:
Struct k
{
Int a: 1
Int: 2/* The two digits cannot be used */
Int B: 3
Int c: 2
};
From the above analysis, we can see that the bit field is essentially a structure type, but its members are allocated by binary.

2. The use of bit domains is the same as that of structure members. The form is generally: Bit domain variable name-bit domain name can be output in various formats.
Main (){
Struct bs
{
Unsigned a: 1;
Unsigned B: 3;
Unsigned c: 4;
} Bit, * pbit;
Bit. a = 1;
Bit. B = 7;
Bit. c = 15;
Printf ("% d, % d, % d \ n", bit. a, bit. B, bit. c );
Pbit = & bit;
Pbit-> a = 0;
Pbit-> B & = 3;
Pbit-> c | = 1;
Printf ("% d, % d, % d \ n", pbit-> a, pbit-> B, pbit-> c );
}

In the preceding example, the bit domain structure bs is defined. The three bit domains are a, B, and c. This section describes the bs type variable bit and the bs type pointer variable pbit. This indicates that pointers can also be used for bit fields.
The program's Lines 9, 10, and 11 assign values to the three single-digit domains. (Note that the value assignment cannot exceed the permitted range of the bit field) The program outputs the content of the three fields in integer format in line 1. Row 3 sends the bit address of the bit field variable to the pointer variable pbit. Row 14th re-assigns a value to bit field a as a pointer and assigns it to 0. Row 15th uses the compound bitwise operator "& =", which is equivalent to 7 in the original value of pbit-> B = pbit-> B & 3-bit Domain B, the bitwise AND operation result of 3 is 3 (111 & 011 = 011, And the decimal value is 3 ). Similarly, the Code uses the compound bitwise operation "| =" in line 1, which is equivalent to pbit-> c = pbit-> c | 1 and the result is 15. The program output the values of the three fields in the pointer mode in Row 3.

Typedef

The C language not only provides a wide range of data types, but also allows you to define the type specifiers by yourself, that is, allow the user to take the "alias" for the data type ". Typedef can be used to complete this function. For example, if there are integer values a and B, the description is as follows: int aa and B, where int Is the type specifier of the integer variable. The complete expression of int Is integer,

To increase the readability of the program, you can use typedef to define the INTEGER specifier as typedef int INTEGER, which can be used to replace int as the type description of the INTEGER variable. For example, INTEGER a and B; it is equivalent to int a and B. It is very convenient to define arrays, pointers, structures, and Other types with typedef, it not only makes the program easy to write but also makes the meaning clearer, thus enhancing readability. For example:
Typedef char NAME [20]; indicates that NAME is of the character array type and the array length is 20.
Then, the variables such as NAME a1, a2, s1, s2 can be used to describe the variables. They are equivalent to char a1 [20], a2 [20], s1 [20], s2 [20]
Another example:
Typedef struct stu {char name [20];
Int age;
Char sex;
} STU;
Define STU to indicate the structure type of stu, and then use STU to describe the structure variables: STU body1, body2;
The general format defined by typedef is: the new type name of the original type name of typedef, the original type name contains the definition part, the new type name is generally expressed in uppercase,
Easy to differentiate. In some cases, macro definitions can be used to replace typedef functions. However, macro definitions are pre-processed, while typedef is compiled, which is more flexible and convenient.

Example:
For example, if you select a moderate color, 1 indicates red, 2 indicates blue, 4 indicates black, and 8 indicates white.
1 = 0000 0001
2 = 0000 0010
4 = 0000 0100
8 = 0000 1000

If you select 2 and 4 (both red and black) then 1 (0000 0001) or 2 (0000 0010) or 4 (0000 0100) = 7 (0000 0101)
If 7 is provided to you, how do you know the options are 1, 2, and 4? The answer is: 7 And four numbers, 1, 2, and 4, respectively, or the result is 7, which indicates that a selected
For example, 7 or 2 = 7, so 1 is selected as 7 or 8 = 15, not 7, so 8 is not selected, so you should know the purpose.

The bit operation method is as follows:

Meaning of operation name
Calculation object type
Calculation Result type object count instance ~ Bit logical non-operation
Integer or simplified integer
1 ~ A & bit logic and arithmetic integer or numeric type
Integer 2 a & B | bit logical or arithmetic integer or numeric integer 2 a | B ^
Bitwise logical exclusive or operation integer or complex integer 1 ^ a <bitwise left shift operation integer or complex integer 2 a <4> bitwise AND shift operation integer or complex integer 2 a> 2

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