C++ STL vector 定义 操作（各种正反向遍历是重点）_c++ 向量里的元素反向循环

（一）了解vector
vector是一个容器，可容纳不同的类型；
常见操作是初始化、push_back/pop_back/insert/erase/clear data to vector、各种正反向遍历、排序与二维定义及遍历。

（二）Test Demo

#include <iostream>
#include <vector>
#include <algorithm>
 
using namespace std;
 
int main()
{
	cout << "*********************Demo1:initial a vector************************" << endl;
	vector<int> a;
	vector<char> b;
	vector<int> c = a, d(a);
	vector<int> e(3, 1), f(3);
	vector<int> g = {1, 2, 3, 4}, h{ 1, 2, 3, 4 };
 
	cout << "*********************Demo2:vector options************************" << endl;
	cout << "(1)push_back/pop_back/insert/erase/clear data to vector" << endl;
	for (size_t i = 0; i < 5; i++)
	{
		a.push_back(i);
	}
	cout << "(2)遍历 vector" << endl;
	for (auto it:a) {
		cout << it;//auto默认为int 故it不用解引用
	}
	cout << endl;
	for (vector<int>::iterator it = a.begin(); it != a.end(); ++it) {
		cout << *it;
	}
	cout << endl;
	cout << "使用反向迭代器" << endl;
	for (auto rit = a.rbegin(); rit != a.rend(); ++rit) {//注意注意迭代器是反向+
		cout << *rit;
	}
	//还可以用a.at(index); or a[index];
	int aaa = a.at(a.size()-1);
	cout << "尾部元素" << aaa << endl;
	
	cout << "*********************Demo3:vector sort************************" << endl;
	vector<int> num{1, 3, 1, 8, 4, 2};
	cout << "sort:";
	sort(num.begin(), num.end());//sort 与reverse 参数必须传入vector的地址，函数定义在algorithm中
	for (auto it : num)
		cout << it;
	cout << endl;
	cout << "reverse:";
	reverse(num.begin(), num.end());
	for (auto it : num)
		cout << it;
	cout << endl;
 
	cout << "*********************Demo4:vector 二维定义************************" << endl;
	vector<vector<int>> twoarray(5, vector<int>(6));//5*6
	for (vector<vector<int>>::iterator it = twoarray.begin(); it != twoarray.end(); ++it) {
		/*for (auto it1 :*it) {
			it1 = int(rand()&0xff) ;
		}*/
		for (vector<int>::iterator it1 = (*it).begin(); it1 != (*it).end(); ++it1) {
			*it1 = int(rand()&0xFF);
		}
	}
	cout << endl;
	for (auto it:twoarray) {
		for (auto it1 : it) {
			cout << it1 << " ";
		}
		cout << endl;
	}
	cout << endl;
 
	return 0;
}