# Vectors in C + +

Source: Internet
Author: User

In C + +, vector is a very useful container, and here is a summary of the container.

1 Basic operations

(2) Create vector object,vector<int> VEC;

(3) Insert number at tail: vec.push_back (a);

(4) Use subscript to access the element,cout<<vec[0]<<endl; remember that the subscript is starting from 0.

(5) Use iterators to access elements.

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

(6) Insert element: Vec.insert (Vec.begin () +i,a); Insert a in front of the first I+1 element;

(7) Delete element: Vec.erase (Vec.begin () +2); Delete 3rd element

Vec.erase (Vec.begin () +i,vec.end () +j); Delete interval [i,j-1]; interval starting from 0

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

(9) Empty: Vec.clear ();

2

Vector elements can not only make int,double,string, but also the structure, but note that the structure should be defined as global, otherwise it will be wrong. Here is a short program code:

`#include <stdio.h>#include<algorithm>#include<vector>#include<iostream>using namespaceStd;typedefstructrect{intID; intlength; intWidthFor vector elements that are structural, you can define a comparison function within the structure, sorted in ascending order of Id,length,width.BOOL operator< (const RECT &a) const{if (id!=a.id)Return id<a.id;Else{if (length!=a.length)Return length<a.length;ElseReturn width<a.width;}}}rect;intmain () {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<<' '<< (*it) .length<<' '<< (*it) .width<<Endl; return 0;}`

3 algorithm

(1) Flip the element with reverse: Requires a header file #include<algorithm>

Reverse (Vec.begin (), Vec.end ()); Flips the element (in a vector, if two iterators are required in a function,

Usually the latter is not included.)

(2) Sorting by using sort: Requires header file #include<algorithm>

Sort (Vec.begin (), Vec.end ());(by default in ascending order, that is, from small to large).

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

To define a sort comparison function:

BOOL Comp (const int &A,CONST int &b)
{
Return a>b;
}
Called When: Sort (Vec.begin (), Vec.end (), Comp), so that it is sorted in descending order.

Vectors in C + +

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