C++学习笔记六：运算符（五种基本运算操作，优先级和结合性）

这一章对操作符进行简单的总结：

1.五种基本运算类型：加减乘除，取余

add, substract, multiply, divide, modulus

int number1{2};
int number2{7};
int result = number1 + number2;
result = number2 - number1 ;
result = number1 - number2;
result = number1 * number2;
result = number2 / number1; // result:3
result = number2 % number1; 

注意：两个int类型相除只会得到int类型的取整

2.优先级与结合性

https://en.cppreference.com/w/cpp/language/operator_precedence

3.前置和后置的++与--

后置的++/--先输出或者赋值原变量，之后再改变原变量

前置的++/--先改变原变量，再做改变后变量的赋值和输出

std::cout << "======Postfix increment and decrement======"<< std::endl;
value = 5;
std::cout << "The value is (incrementing) : " << value++ << std::endl; // 5
std::cout << "The value is : " << value << std::endl; // 6
std::cout << std::endl;
value = 5; //Reset value to 5
std::cout << "The value is (decrementing) : " << value-- << std::endl; //5
std::cout << "The value is : " << value << std::endl; // 4

std::cout << "======Prefix increment and decrement======"<< std::endl;
value = 5;
++value;
std::cout << "The value is (prefix++) : " << value << std::endl; // 6
value = 5;
std::cout << "The value is (prefix++ in place) : " << ++value << std::endl; // 6
std::cout << std::endl;

4.复合运算符

复合运算符同时完成运算和赋值的操作。

int value {45};
value +=5;
value -=5;
value *=2;
value /= 3;
value %= 11;

5.比较运算符

int number1 {20};
int number2 {20};

std::cout << std::boolalpha ; // Make bool show up as true/false instead of 1/0
//Stress the need for parentheses here
std::cout << "number1 < number2 : " << (number1 < number2) << std::endl;
std::cout << "number1 <= number2 : " << (number1 <= number2) << std::endl;
std::cout << "number1 > number2 : " << (number1 > number2) << std::endl;
std::cout << "number1 >= number2 : " << (number1 >= number2) << std::endl;
std::cout << "number1 == number2 : " << (number1 == number2) << std::endl;
std::cout << "number1 != number2 : " << (number1 != number2) << std::endl;

在输出比较结果的时候记得加上括号。<<的优先级高于比较运算符。

6.逻辑运算符

AND && 全真才真

OR || 一真即真

NOT !

这三个逻辑运算符联合使用记得优先级：NOT>AND>OR

bool a {true};
bool b {true};
bool c {false};

std::cout << std::boolalpha;
std::cout << (!a || b && c) << std::endl;
// !a: false, b && c: false, result: false