How to Add Element at the End of a Vector in C++?

Vector allows fast insertion and deletion at the end. In this article, we will learn different ways to add an element at the end of the vector.

The easiest way to add an element at the end of vector is by using vector push_back() function. Let’s take a look at a simple example:

#include <bits/stdc++.h>
using namespace std;
int main() {
    vector<int> v;
    // Inserting elements at end of vector
    v.push_back(1);
    v.push_back(7);
    v.push_back(9);
    for (auto i : v)
        cout << i << " ";
    return 0;
}

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The push_back() function adds an element at the end of vector and increment the size of vector by 1.

There are also some other methods in C++ to add an element at the end of vector. Following are the ways:

Using Vector emplace_back()

The vector emplace_back() method is similar to the vector push_back() method but it avoids creating temporary copies by constructing the element to be inserted in-plane inside the vector.

#include <bits/stdc++.h>
using namespace std;
int main() {
    vector<int> v;
    // Inserting elements at end of vector
    v.emplace_back(1);
    v.emplace_back(7);
    v.emplace_back(9);
    for (auto i : v)
        cout << i << " ";
    return 0;
}

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Using Vector insert()

The vector insert() method can insert an element at any position in the vector including the end.

#include <bits/stdc++.h>
using namespace std;
int main() {
    vector<int> v;
    // Inserting an element at end of vector
    v.insert(v.end(), 1);
    v.insert(v.end(), 7);
    v.insert(v.end(), 9);
    for (auto i : v)
        cout << i << " ";
    return 0;
}

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Explanation: The vector insert() function takes the iterator to where the element is to be inserted as first parameter, which in this case is vector end() iterator and value to insert as second parameter.

Using Vector [] Operator

The [] operator in vector is used to access and update the already present elements. So, first create an element at the end of the vector by increase the size of vector using vector resize() function and then assign an element at the end of vector.

#include <bits/stdc++.h>
using namespace std;
int main() {
    vector<int> v = {1, 7};
    // Increasing the size of vector
    v.resize(v.size() + 1);
    // Assign the element at end of vector
    v.back() = 9;
    for (auto i : v)
        cout << i << " ";
    return 0;
}

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Using back_inserter()

The back_intserter() function resize the given array by adding an element with the default value at the and return the iterator to this element. This iterator can be then dereferenced to assign some new value.

#include <bits/stdc++.h>
using namespace std;
int main() {
    vector<int> v;
    // Inserting an element at end of vector
  	*back_inserter(v) = 1;
    *back_inserter(v) = 7;
    *back_inserter(v) = 9;
    for (auto i : v)
        cout << i << " ";
    return 0;
}

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This method is mostly used with STL algorithms for containers that supports the push_back() operation.