What is the usage of c++ vector

c The usage of vector is: 1. Create vector object; 2. Insert numbers at the end; 3. Use subscripts to access elements; 4. Use iterators to access elements; 5. Insert elements; 6.) Delete elements, etc. wait.

In c, vector is a very useful container. The usage of c vector is:

1. Basic operations

(1)Header file#include.

(2)Create vector object, vector vec;

( 3) Insert numbers at the end: vec.push_back(a);

(4) Use subscripts to access elements, cout

(5) Use an iterator to access elements.

vector<int>::iterator it;
for(it=vec.begin();it!=vec.end();it++)
    cout<<*it<<endl;

(6) Insert elements:

vec.insert(vec.begin()+i,a);

Insert a in front of the i 1st element;

(7) Delete element:

vec.erase(vec.begin()+2);

Delete the 3rd element

vec.erase(vec.begin()+i,vec.end()+j);

Delete interval [i,j-1]; the interval starts from 0

(8) Vector size: vec.size();

(9) Clear: vec.clear();

2, The elements of vector can not only be int, double, string, but also structures, but please note: the structure must be defined as global, otherwise an error will occur. The following is a short program code:

#include<stdio.h>
#include<algorithm>
#include<vector>
#include<iostream>
using namespace std;
typedef struct rect
{
    int id;
    int length;
    int width;
　　//对于向量元素是结构体的，可在结构体内部定义比较函数，下面按照id,length,width升序排序。
　　bool operator< (const rect &a)  const
    {
        if(id!=a.id)
            return id<a.id;
        else
        {
            if(length!=a.length)
                return length<a.length;
            else
                return width<a.width;
        }
    }
}Rect;
int main()
{
    vector<Rect> vec;
    Rect rect;
    rect.id=1;
    rect.length=2;
    rect.width=3;
    vec.push_back(rect);
    vector<Rect>::iterator it=vec.begin();
    cout<<(*it).id<<&#39; &#39;<<(*it).length<<&#39; &#39;<<(*it).width<<endl;    
return 0;
}

3. Algorithm

(1), use reverse to flip elements: header file required #include

reverse(vec.begin(),vec.end());

Flip the elements (in vector, if two iterators are required in a function, usually neither of the latter is included.)

(2), use sort to sort: header file is required #include< ;algorithm>,

sort(vec.begin(),vec.end());

(The default is to sort in ascending order, that is, from small to large).

You can compare in descending order by overriding the sort comparison function, as follows:

Definition Sorting comparison function:

bool Comp(const int &a,const int &b)
{
    return a>b;
}

When called: sort(vec.begin(),vec.end(),Comp), this will sort in descending order.

Related learning recommendations: C video tutorial

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