how to initialize a vector in c++

Question

Problem:

I am a newbie in the world of programming. I want to know the easiest way to initialize a vector in c++. If possible give me the codes too.

Thanks in advance

Answer 1

Welcome to the fun world of programming, mate.

There are a couple of ways to initialize a vector in c++. As far as the easiest way is your concern I recommend you to use this way below.

#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    // Create an empty vector 
    vector<int> vect;   
    vect.push_back(5); 
    vect.push_back(10); 
    vect.push_back(20); 
  
    for (int n : vect) 
        cout << n << " "; 
  
    return 0;
}

or,

#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    vector<int> vect{ 5, 10, 20 }; 
  
    for (int n : vect) 
        cout << n << " "; 
  
    return 0; 
}

In both cases, your output should be 5,10, and 20.

Answer 2

One method would be to use the array to initialize the vector

static const int arr[] = {16,2,77,29};
vector<int> vec (arr, arr + sizeof(arr) / sizeof(arr[0]) );

Initializing by pushing values one by one :

// 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; 
} 

Specifying size and initializing all values :

// 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; 
} 

Initializing like arrays :

// 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; 
} 

Initializing from an array :

// 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; 
} 

Initializing from another vector :

// 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; 
}