C++ Primer （第五版）-第四章 表达式

一、概述

二、内容

4.1、基础

一元运算符（unary operator）：取地址符（&）和解引用（）
二元运算符 (binary operator)： 相等运算符（==）和乘法运算符（）
首先理解运算符的优先级、结合律以及运算对象的求值顺序。
运算对象的转换（类型转换）
重载运算符 ：例如IO库中>>和<<,以及命名空间引用string :: 和 vector<> 、迭代器等

难点：decltype

优先级和结合律

#include <iostream>
using std::cout; using std::endl;

int main() 
{
	cout << 6 + 3 * 4 / 2 + 2 << endl;

	// parentheses in this expression match default precedence and associativity
	cout << ((6 + ((3 * 4) / 2)) + 2) << endl; // prints 14

	int temp = 3 * 4;         // 12
	int temp2 = temp / 2;     // 6
	int temp3 = temp2 + 6;    // 12
	int result = temp3 + 2;   // 14
	cout << result << endl;

	// parentheses result in alternative groupings
	cout << (6 + 3) * (4 / 2 + 2) << endl;     // prints 36
	cout << ((6 + 3) * 4) / 2 + 2 << endl;     // prints 20
	cout << 6 + 3 * 4 / (2 + 2) << endl;       // prints 9

    return 0;
}

4.2、算术运算符

#include <iostream>
using std::cout; using std::endl;

int main()
{
	cout << -30 * 3 + 21 / 5 << endl;
	
	cout << -30 + 3 * 21 / 5 << endl;
	
	cout << 30 / 3 * 21 % 5 << endl;
	
	cout << 30 / 3 * 21 % 4 << endl;
	
	cout << -30 / 3 * 21 % 4 << endl;
	
	cout << 12 / 3 * 4 + 5 * 15 + 24 % 4 / 2 << endl;
	
	return 0;
}

4.3逻辑和关系运算符

4.4赋值运算符

C++11中允许用花括号进行初始值列表作为赋值语句的右侧运算对象

复合赋值运算符

4.5、递增和递减运算符

++i;
i++;

#include <iostream>
using std::cout; using std::endl;

int main() 
{
	int i = 0, j;
	j = ++i; // j = 1, i = 1: prefix yields the incremented value
	cout << i << " " << j << endl;

	j = i++; // j = 1, i = 2: postfix yields the unincremented value
	cout << i << " " << j << endl;

	return 0;
}

4.6成员访问运算符

4.7、条件运算符

#include <iostream>
using std::cin; using std::cout; using std::endl;

#include <string>
using std::string;

#include <vector>
using std::vector;

vector<unsigned> grades;

int main()
{
	unsigned i;
	while (cin >> i)
		grades.push_back(i);

	for (auto grade : grades) {  // for each grade in grades
		// set the initial grade as pass or fail
		string finalgrade = (grade < 60) ?  "fail" : "pass";

		finalgrade = (grade > 90) ? "high pass"
				                  : (grade < 60) ? "fail" : "pass";

		cout << grade << " " + finalgrade << endl;
	}

	return 0;
}

4.8、位运算符

4.9、sizeof运算符

#include "Version_test.h"

#include <iostream>
using std::cout; using std::endl;

#include "Sales_data.h"

int main() 
{
	Sales_data data, *p;
	sizeof(Sales_data); // size required to hold an object of type Sales_data 
	sizeof data; // size of data's type, i.e., sizeof(Sales_data)
	sizeof p;    // size of a pointer
	sizeof *p;   // size of the type to which p points, i.e., sizeof(Sales_data)
	sizeof data.revenue; // size of the type of Sales_data's revenue member 
#ifdef SIZEOF_MEMBER
	sizeof Sales_data::revenue; // alternative way to get the size of revenue
#else
	sizeof Sales_data().revenue; // use an object
#endif
	
	cout << "short: " << sizeof(short) << "\n"
	     << "short[3]: " << sizeof(short[3]) << "\n"
	     << "short*: " << sizeof(short*) << "\n"
	     << "short&: " << sizeof(short&) << endl;
	
	cout << endl; 
	
	cout << "int: " << sizeof(int) << "\n"
	     << "int[3]: " << sizeof(int[3]) << "\n"
	     << "int*: " << sizeof(int*) << "\n"
	     << "int&: " << sizeof(int&) << endl;
	
	cout << endl; 
	
	cout << "Sales_data: " << sizeof(Sales_data) << "\n"
	     << "Sales_data[3]: " << sizeof(Sales_data[3]) << "\n"
	     << "Sales_data*: " << sizeof(Sales_data*) << "\n"
	     << "Sales_data&: " << sizeof(Sales_data&) << endl;
	
#ifdef SIZEOF_MEMBER
	cout << "Sales_data::revenue: " << sizeof Sales_data::revenue << "\n"
#else
	cout << "Sales_data().revenue: " << sizeof Sales_data().revenue << "\n"
	     << "data.revenue: " << sizeof data.revenue << endl;
#endif

	int x[10];   
	int *ip = x;

	// number of elements in x
	cout << sizeof(x)/sizeof(*x) << endl;

	// divides sizeof a pointer by sizeof an int
	cout << sizeof(ip)/sizeof(*ip) << endl;
	
	return 0;
}

4.10、逗号运算符

#include <cstddef>
using std::size_t;

#include <vector>
using std::vector;

#include <iostream>
using std::cout; using std::endl;

int main()
{
    
    vector<int> ivec;                // empty vector
    int cnt = 10;
    // add elements 10 . . . 1 to ivec
    while (cnt > 0)
        ivec.push_back(cnt--);       // int postfix decrement

    auto iter = ivec.begin();
    // prints 10 9 8 . . . 1 
    while (iter != ivec.end())
        cout << *iter++ << endl; // iterator postfix increment

	vector<int> vec2(10, 0);  // ten elements initially all 0
    cnt = vec2.size();
    // assign values from size . . . 1 to the elements in vec2
    for(vector<int>::size_type ix = 0; 
                    ix != vec2.size(); ++ix, --cnt)   
        vec2[ix] = cnt;

    iter = vec2.begin();
    // prints 10 9 8 . . . 1 
    while (iter != vec2.end())
        cout << *iter++ << endl; // iterator postfix increment

    return 0;
}

4.11、 类型转换

4.12 运算符优先级

4.13、小结

4.14、术语表