How to Replace a Value in an Array in C++?

In C++, an array is a data structure that is used to store multiple values of similar data types in a contiguous memory location. In this article, we will learn how to replace a value in an array in C++.

Example:

Input:
arr: {10 20 30 30 20 10 10 20}
Element_to_replace= 20
replacement=99

Output:
Array after replacement: {10 99 30 30 99 10 10 99}

Replace Element of an Array With Another in C++

To replace an element of an array, we can use the std::replace() that assigns new_value to all the elements in the range [first, last) that are equal to old_value. This function uses the operator == to compare the individual elements to the old_value.

Syntax of std::replace

void replace(first, last, old_value, new_value)

Here,

• first, last: Forward iterators to the initial and final positions in a sequence of elements.
• old_value: Value to be replaced.
• new_value: Replacement value.

C++ Program to Replace a Value in an Array

The below program demonstrates how we can replace a value in an array with another value.

// C++ Program to find and replace the value

#include <algorithm>
#include <iostream>
using namespace std;

int main()
{
    int arr[] = { 10, 20, 30, 30, 20, 10, 10, 20 };
    int n = sizeof(arr) / sizeof(arr[0]);

    // variable containing the old and new values
    int old_val = 20, new_val = 99;

    // print old array
    cout << "Original Array:";
    for (int i = 0; i < n; i++)
        cout << ' ' << arr[i];
    cout << endl;

    // Function used to replace the values
    replace(arr, arr + n, old_val, new_val);

    // new array after using std::replace
    cout << "New Array:";
    for (int i = 0; i < n; i++)
        cout << ' ' << arr[i];
    cout << endl;

    return 0;
}

Original Array: 10 20 30 30 20 10 10 20
New Array: 10 99 30 30 99 10 10 99

Time Complexity: O(N)
Auxilliary Space: O(1)