Check out example codes for "declare vectors c++". It will help you in understanding the concepts better.

Code Example 1

// 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; 
}

Code Example 2

std::vector<type> name;

Code Example 3

// CPP program to create an empty vector 
// and push values one by one. 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    // Create an empty vector 
    vector<int> vect;  
     
    vect.push_back(10); 
    vect.push_back(20); 
    vect.push_back(30); 
  
    for (int x : vect) 
        cout << x << " "; 
  
    return 0; 
}

Code Example 4

// First include the vector library:
#include <vector>

// The syntax to create a vector looks like this:
std::vector<type> name;

// We can create & initialize "lol" vector with specific values:
std::vector<double> lol = {66.666, -420.69};

// it would look like this: 66.666 | -420.69

Code Example 5

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. */

Code Example 6

// CPP program to initialize a vector like 
// an array. 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    vector<int> vect{ 10, 20, 30 }; 
  
    for (int x : vect) 
        cout << x << " "; 
  
    return 0; 
}

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