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C++ <cmath>

C++ Bitwise Operators

C++ operator precedence and associativity

In this tutorial, we will learn about C ++operator precedence and associativity.

C ++operator precedence

If there are multiple operators in a single expression, they will not be evaluated simultaneously. Instead, those withhigher precedenceoperators will first evaluate their operands.

Let's look at an example:

int x =　5　-　17　*　6;

Here, the multiplication operator * has a higher precedence than the subtraction operator - . Therefore,17 * 6first evaluating.

the result, the above expression is equivalent to

int x =　5　-　(17　*　6);

if we want to evaluate first5 - 17and must be placed insideinside the parentheses:

int x = (5　-　17)　*　6;

Example1operator precedence

Example

#include <iostream>
using namespace std;
int main() {
　　//　first evaluates17　*　6
　　int num1　=　5　-　17　*　6;
　　//with num1the equivalent expression
　　int num2　=　5　-　(17　*　6);
　　//forces the compiler to evaluate5-17
　　int num3　= (5　-　17)　*　6;
　　cout << "num"1　=" << num1　<< endl;
　　cout << "num"2　=" << num2　<< endl;
　　cout << "num"3　=" << num3　<< endl;
　　return 0;
}

Output Result

num1　=　-97
num2　=　-97
num3　=　-72

Note:Since C ++There are many operators with multiple precedences in it, so it is strongly recommended that we useparenthesesto make the code more readable.

C ++operator precedence table

The following table shows the C ++of the operators. Precedence1represents the highest precedence operator, while the precedence17represents the lowest precedence operator.

precedence	operator	description	associativity
1	::	scope	from left to right
2	a++ a-- type( ) type{ } a( ) a[ ] . ->	postfix/postfix increment postfix/postfix decrement function-style cast function-style cast function call index Accessing the member from the object Accessing the member from the object ptr	from left to right
3	++a --a +a -a ! ~ (type) *a &a sizeof co_await new new[ ] delete delete[]	prefix increment prefix decrement positive negative logical NOT bitwise NOT C-style cast indirect (dereference) get address get size await expression dynamic memory allocation dynamic memory release	from right to left
4	.* ->*	member object selector member pointer selector	from left to right
5	a * b a / b a % b	multiplication division modulus	from left to right
6	a + b a - b	plus minus	from left to right
7	<< >>	bitwise left shift bitwise right shift	from left to right
8	<=>	three-way comparison operator	from left to right
9	< <= > >=	less less than or equal greater greater than or equal	from left to right
10	== !=	equal not equal	from left to right
11	&	bitwise and	from left to right
12	^	bitwise xor	from left to right
13	\|	bitwise or	from left to right
14	&&	logical and	from left to right
15	\|\|	logical or	from left to right
16	a ? b : c throw co_yield = += -= *= /= %= <<= >>= &= ^= \|=	ternary conditional operator throw operator yield expression (C++ 2(0) assignment addition assignment subtraction assignment multiplication assignment division distribution modulus assignment bitwise left shift assignment bitwise right shift assignment bitwise and assignment bitwise xor assignment bitwise or assignment	from right to left
17	,	comma operator	from left to right

associationThe property of this will be discussed later.

C ++The associativity of an operator

The associativity of an operator is the calculation of the expression'sdirection. For example,

Example

int a =　1;
int b =　4;
//　a =　4
a = b;

Please see a=4; statement. The associativity of the equal (=) operator is from right to left. Therefore, the value of b is assigned to a.

Similarly, multiple operators can have the same precedence (as shown in the table above). When multiple operators with the same precedence are used in an expression, they will be evaluated based on theirassociativityevaluate them.

Example

int a =　1;
int b =　4;
b　+= a　-=　6;

operator+and-The equal (=) operator has the same precedence. Since the associativity of these operators is from right to left, this is the evaluation method of the last statement.

a -= 6 will be evaluated first. Therefore, a will be-5
Then, b += -5will be evaluated. Therefore, b will be-1

Example2: Associativity of Operators

Example

#include <iostream>
using namespace std;
int main() {
　　int a =　1;
　　int b =　4;
//　a　-=　6　First, evaluate
　　b　+= a　-=　6;
　　cout << "a = " << a << endl;
　　cout << "b = " << b;
}

Output Result

a =　-5
b =　-1

C++ Bitwise Operators