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

Code Example 1

// CPP program to create an empty vector 
// and push values one by one. 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    int n = 3; 
  
    // Create a vector of size n with 
    // all values as 10. 
    vector<int> vect(n, 10); 
  
    for (int x : vect) 
        cout << x << " "; 
  
    return 0; 
}

Code Example 2

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

Code Example 3

//Note: any data type can be used in template.
std::vector<typename T> vectorName;

Code Example 4

// 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 5

// 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 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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