How to find the length of the vector in C++

Like dynamic arrays, vectors can automatically adjust their size when an element is added or removed, and the container manages its storage.

Because vector items are stored in contiguous storage, iterators can access and traverse them.

Data is appended to vectors at the end. Inserting at the end takes longer because the array may need to be enlarged often.

The final data element cannot be removed because no resizing is involved. When a data element is added or deleted at the start or the halfway point, time is linear.

A vector is a container that sequentially stores elements rather than using an index. Because a vector is dynamic, the size grows as elements are added.

Vector uses more memory. Accessing items in Vector takes longer.

The vector is realized as a dynamic array with an interface. The interface used is the list interface.

Length of C++ vector

Use the size() method on a C++ vector to determine its size or length.

The size() function returns the vector's element count. The element count is referred to as the length of the vector.

Example 1

Finding the vector length using the size() method in C++. In the C++ program below, a vector of integers is created, adding some data members to the vector. After adding the data elements, the size() method determines the vector's length or the vector size.

The following program code will display the length of the vector named count.

#include <iostream>
#include <vector>
using namespace std ;
 
int main() {
   vector<int> count ;
   count.push_back(2) ;
   count.push_back(8) ;
   count.push_back(5) ;
   count.push_back(10) ;
   count.push_back(54) ;
   count.push_back(100) ;
   count.push_back(99) ;
   cout << "The length of the vector is: " ;
   cout << count.size() ;
}

Output

Example 2

Size of the vector that is empty.

In the C++ program below,  An empty vector is created. The empty vector is of integers. After defining the vector,   the size() method is used to determine the length or size of the vector. 

The result of size() should be 0.

#include <iostream>
#include <vector>
using namespace std ;
 
int main() {
   vector<int> vec ; // vec is the vector variable
   cout << "The vector size is " ;// Using size() method to display 
                                  //the length of the vector
   cout << vec.size() ;
}

Example 3

Determining the size of the vector using the foreach loop.

C++ foreach loop helps in finding the length or size of the vector. First, define the vector, give it a name, and initialize it with elements. The below program initializes the vector and uses the foreach loop. Then, using the “l” variable with a zero initial value, count the number of elements in the vector. Next, using the “l” variable with a zero initial value, count the number of elements in the vector.

To iterate over the elements of the vector and increment the counter during each iteration, use the foreach loop.

#include <iostream>
#include <vector>
using namespace std ;
 
int main() {
   vector<int> vec; //variable "vec" is the vector variable
   vec.push_back(7) ;
   vec.push_back(18) ;
   vec.push_back(45) ;
   vec.push_back(333) ;
   vec.push_back(17) ;
 
   int l = 0 ;  //Using the variable "l" to display the length
   for (int element: vec)
      l++ ; 
   cout << "The length of the vector is " ;
   cout << l ; //prints the length of the vector
}

Example 4

Displaying the length of the vector. The user gives the vector elements as user input.

#include<bits/stdc++.h>
using namespace std ;


//main function
int main() {
    int input ; 
    cin>>input; // taking the size of the vector as the user input
    int a ;
    vector<int> vec;
    // the size of the vector can also be mentioned here.
    // Another way to mention the size of the vector is vector<int> v(input);
    for(int i=0 ; i<input ; i++)
    {
        cin>>a ;
        vec.push_back(a);
    }
    for(auto &p : vec)
    {
        cout<<p<<" " ;
    }
    cout << "\nThe given length of the vector is " ;
    cout << vec.size() ;
    cout<<endl ;
    return 0 ;
}

Output 1

Output 2