How to initialize a vector in C++?

Initialization vector can be done in many ways

1) Initialize a vector by push_back() method

Algorithm

Begin
   Declare v of vector type.
   Call push_back() function to insert values into vector v.
   Print “Vector elements:”.
   for (int a : v)
      print all the elements of variable a.
End.

Example

 Live Demo

#include<iostream>
#include <bits/stdc++.h>
using namespace std;
int main() {
   vector<int> v;
   v.push_back(6);
   v.push_back(7);
   v.push_back(10);
   v.push_back(12);
   cout<<"Vector elements:"<<endl;
   for (int a : v)
      cout << a << " ";
   return 0;
}

Output

Vector elements:
6 7 10 12

2) Initialize a vector by array

Algorithm

Begin
   Create a vector v.
   Initialize vector like array.
   Print the elements.
End.

Example

 Live Demo

#include <bits/stdc++.h>
using namespace std;
int main() {
   vector<int> v{ 1, 2, 3, 4, 5, 6, 7 };
   cout<<"vector elements:"<<endl;
   for (int a : v)
      cout << a << " ";
   return 0;
}

Output

vector elements:
1 2 3 4 5 6 7

3) Initialize a vector from another vector

Algorithm

Begin
   Create a vector v1.
   Initialize vector v1 by array.
   Initialize vector v2 by v1.
   Print the elements.
End.

Example

 Live Demo

#include<iostream>
#include <bits/stdc++.h>
using namespace std;
int main() {
   vector<int> v1{ 1, 2, 3, 4, 5, 6, 7 };
   vector<int> v2(v1.begin(), v1.end());
   cout<<"vector elements:"<<endl;
   for (int a : v2)
      cout << a << " ";
   return 0;
}

Output

vector elements:
1 2 3 4 5 6 7

4) Initialize a vector by specifying size and elements

Algorithm

Begin
   Initialize a variable s.
   Create a vector v with size s and all values with 7.
   Initialize vector v1 by array.
   Initialize vector v2 by v1.
   Print the elements.
End.

Example

 Live Demo

#include<iostream>
#include <bits/stdc++.h>
using namespace std;
int main() {
   int s= 5;
   vector<int> v(s, 7);
   cout<<"vector elements:"<<endl;
   for (int a : v)
      cout << a << " ";
   return 0;
}

Output

vector elements:
7 7 7 7 7