vectors c++

// CPP program to create an empty vector 
// and push values one by one. 
#include <vector>

using namespace std;
int main() 
{ 
    // Create an empty vector 
    vector<int> vect;  
    //add/push an integer to the end of the vector
    vect.push_back(10); 
	//to traverse and print the vector from start to finish
    for (int x : vect) 
        cout << x << " ";

    return 0; 
}

#include <vector>

int main() {
  std::vector<int> v;
  v.push_back(10); // v = [10];
  v.push_back(20); // v = [10, 20];
  
  v.pop_back(); // v = [10];
  v.push_back(30); // v = [10, 30];
  
  auto it = v.begin();
  int x = *it; // x = 10;
  ++it;
  int y = *it; // y = 30
  ++it;
  bool is_end = it == v.end(); // is_end = true
  
  return 0;
}

// C++ program to illustrate the 
// Modifiers in vector 
#include <bits/stdc++.h> 
#include <vector> 
using namespace std; 
  
int main() 
{ 
    // Assign vector 
    vector<int> v; 
  
    // fill the array with 10 five times 
    v.assign(5, 10); 
  
    cout << "The vector elements are: "; 
    for (int i = 0; i < v.size(); i++) 
        cout << v[i] << " "; 
  
    // inserts 15 to the last position 
    v.push_back(15); 
    int n = v.size(); 
    cout << "\nThe last element is: " << v[n - 1]; 
  
    // removes last element 
    v.pop_back(); 
  
    // prints the vector 
    cout << "\nThe vector elements are: "; 
    for (int i = 0; i < v.size(); i++) 
        cout << v[i] << " "; 
  
    // inserts 5 at the beginning 
    v.insert(v.begin(), 5); 
  
    cout << "\nThe first element is: " << v[0]; 
  
    // removes the first element 
    v.erase(v.begin()); 
  
    cout << "\nThe first element is: " << v[0]; 
  
    // inserts at the beginning 
    v.emplace(v.begin(), 5); 
    cout << "\nThe first element is: " << v[0]; 
  
    // Inserts 20 at the end 
    v.emplace_back(20); 
    n = v.size(); 
    cout << "\nThe last element is: " << v[n - 1]; 
  
    // erases the vector 
    v.clear(); 
    cout << "\nVector size after erase(): " << v.size(); 
  
    // two vector to perform swap 
    vector<int> v1, v2; 
    v1.push_back(1); 
    v1.push_back(2); 
    v2.push_back(3); 
    v2.push_back(4); 
  
    cout << "\n\nVector 1: "; 
    for (int i = 0; i < v1.size(); i++) 
        cout << v1[i] << " "; 
  
    cout << "\nVector 2: "; 
    for (int i = 0; i < v2.size(); i++) 
        cout << v2[i] << " "; 
  
    // Swaps v1 and v2 
    v1.swap(v2); 
  
    cout << "\nAfter Swap \nVector 1: "; 
    for (int i = 0; i < v1.size(); i++) 
        cout << v1[i] << " "; 
  
    cout << "\nVector 2: "; 
    for (int i = 0; i < v2.size(); i++) 
        cout << v2[i] << " "; 
} 

// CPP program to initialize a vector from 
// another vector. 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    vector<int> vect1{ 10, 20, 30 }; 
  
    vector<int> vect2(vect1.begin(), vect1.end()); 
  
    for (int x : vect2) 
        cout << x << " "; 
  
    return 0; 
} 

// C++ program to illustrate the 
// capacity function in vector 
#include <iostream> 
#include <vector> // add the import to use vectors
  
using namespace std; 
  
int main() 
{ 
    vector<int> g1; 
  
    for (int i = 1; i <= 5; i++) 
        g1.push_back(i); 
  
    cout << "Size : " << g1.size(); 
    cout << "\nCapacity : " << g1.capacity(); 
    cout << "\nMax_Size : " << g1.max_size(); 
  
    // resizes the vector size to 4 
    g1.resize(4); 
  
    // prints the vector size after resize() 
    cout << "\nSize : " << g1.size(); 
  
    // checks if the vector is empty or not 
    if (g1.empty() == false) 
        cout << "\nVector is not empty"; 
    else
        cout << "\nVector is empty"; 
  
    // Shrinks the vector 
    g1.shrink_to_fit(); 
    cout << "\nVector elements are: "; 
    for (auto it = g1.begin(); it != g1.end(); it++) 
        cout << *it << " "; 
  
    return 0; 
} 

vector<int> vec;
//Creates an empty (size 0) vector
 

vector<int> vec(4);
//Creates a vector with 4 elements.

/*Each element is initialised to zero.
If this were a vector of strings, each
string would be empty. */

vector<int> vec(4, 42);

/*Creates a vector with 4 elements.
Each element is initialised to 42. */


vector<int> vec(4, 42);
vector<int> vec2(vec);

/*The second line creates a new vector, copying each element from the
vec into vec2. */

Vectors are same as dynamic arrays with the ability to resize itself automatically when an element is inserted or deleted, with their storage being handled automatically by the container. Vector elements are placed in contiguous storage so that they can be accessed and traversed using iterators. In vectors, data is inserted at the end. Inserting at the end takes differential time, as sometimes there may be a need of extending the array. Removing the last element takes only constant time because no resizing happens. Inserting and erasing at the beginning or in the middle is linear in time.