How to Remove an Element from Array in C++?

In C++, removing an element from an array is tricky because we cannot modify the memory space occupied by the array. So, we pseudo delete the element by moving it to the end of the array and reducing the size. In this article, we will learn how to remove a value from an array in C++.

Examples

Input: arr[] = {3, 1, 2, 5, 90}, val = 2
Output: 3 1 5 90
Explanation: As element 2 is removed from an array.

Input: arr[] = {3, 1, 2, 5, 90}, val = 90
Output: 3, 1, 2, 5
Explanation: As element 90 is removed from an array.

There are 2 primary ways to remove the elements using remove function in C++:

Remove Element Using Library Function

C++ STL provides std::remove() method using which we can move the elements to be removed to the end of the array and update the variable that keeps the track of the size of the array (as we cannot remove the memory occupied by fixed size array elements).

Syntax

std::remove(first, last, key)

where,

• first: Iterator to the first element of the range.
• last: Iterator to the element just after the last element of the given range.
• key: Element to be removed.

std::remove() function returns an iterator to new logical end of the array that contains only those elements that are not removed.

Example

// C++ Program to remove an element from the
// array using std::remove()
#include <bits/stdc++.h>
using namespace std;

int main() {
    int arr[] = {3, 1, 2, 5, 90};
    int n = sizeof(arr) / sizeof(arr[0]);

    // The element which we have to delete
    int key = 2;

    // Use std::remove() to move all occurrences
    // of 2 to the end
    auto end = std::remove(arr, arr + n, key);

    // Calculate the new size of the array
  	// after removal
    n = end - arr;

    for (int i = 0; i < n; i++)
        cout << arr[i] << " ";
    return 0;
}

3 1 5 90 

Time Complexity: O(n), where n is the number of elements in the array.
Auxiliary Space: O(1)

Remove Element Manually Using Loop

To remove a value from an array in C++, we first search the position of the element to be removed, then move elements that are on the right side of this element to one position towards the front (i.e. towards the left). Then decrement the array size variable. This effectively deletes the from the array.

Code Implementation

// C++ program to illustrate how to remove a 
// given element from an array
#include <bits/stdc++.h>
using namespace std;

int main() {
    int arr[] = {3, 1, 2, 5, 90};
    int n = sizeof(arr) / sizeof(arr[0]);

    // The element which we have to delete
    int key = 2;

    // Search key in array
    for (int i = 0; i < n; i++) {

        // If key is found in array
        if (arr[i] == key) {
          
                // Reduce size of array and move all
                // elements one space towards left
                n = n - 1;
                for (int j = i; j < n; j++)
                    arr[j] = arr[j + 1];
            break;
        }
    }

    for (int i = 0; i < n; i++)
        cout << arr[i] << " ";
    return 0;
}

3 1 5 90 

Time Complexity: O(n), where n is the number of elements in the array.
Auxiliary Space: O(1)