C++ Vector : Basics Of Vector in C++ STL

In C++, Vector is unlike array, it stores different data types such as int, double, string, float, etc. It works like the dynamic array with the ability to resize automatically itself. Vector stores data in the contiguous memory location. Two functions are needed to traverse from starting to end that is begin() and end() functions.

                             

Syntax of the vector declaration:-

            vector<data_type> variable_name (number_of_elements); 

Here number_of_elements is optional, we can also declare a vector with empty vector that contains zero elements. The data_type in the angle-brackets indicates any type of data type which is valid in c++.

Vector declaration examples:-

vector<int> numbers (10);

//In this example, we declared a vector name number of 10 integers.

vector<string> names; 

//In this, a vector name declared of string.

In every program of the vector it is necessary to add the header file at the top of the program. We must provide the appropriate #include directive at the top, since vector is a Standard Library, not in build in part of a core language. We must specify the vector header file such as

 

      #include<vector>

After a vector has been declared specifying a certain number of elements, we can refer to individual elements in the vector using square brackets to provide a subscript or index, as shown below:-

   

        numbers[10];

Some algorithms are used in the Standard library such as sort(), reverse(), random_shuffle(), max_element(), min_element(),etc. So, it is necessary to add a header file that is #include<algorithm>.

For iterating the for loop or any task which star from the beginning of the vector to the end, vector uses the begin() function and end() function.

A simple example to illustrate the vector:

 

#include<iostream>

#include<vector>

#include<algorithm>

using namespace std;

int main()

{

   //Declaration of vector container

  vector<int> numbers(5);

   cout<<"Enter the 5 values:-";

   

   for(vector<int>::iterator it = numbers.begin(); it! = numbers.end(); it++)

   {

       cin>>*it;

   }

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

   cout<<"After sorting:-"

    for(vector<int>::iterator it = numbers.begin(); it! = numbers.end(); it++)

    {

       cout<<*it<<" ";

    }

   return 0; 

}

Output:-

Enter the 5 values:-

8

2

9

1

10

After sorting:-

1 2 8 9 10

This is the sorting of the 5 numbers, this program contains an iterator which is used to iterate the for loop from beginning of the vector to its end. In this header file are used such as #include<iostream>, #include<vector>, #include<algorithm>, these are necessary to execute all the code of the programs because the core language have not build in vector in it.