How to Find All Indexes of an Element in an Array in C++?

In C++, an array is a collection of elements of the same type placed in contiguous memory locations. In this article, we will learn how to find all indexes of a specific element in an array in C++.

Example:

Input: 
myArray = {1, 2, 2, 3, 3, 3, 4, 4, 4, 4}; 
target = 3

Output: 
The element 3 occurred at indices: 3 4 5

Finding All Indexes of an Element in an Array in C++

 To find all indexes of an element in an array in C++, we have to iterate through the whole array looking for the target. If the target is found, we will print it. Otherwise, we can continue to the next loop.

C++ Program To Find All Indexes of an Element in an Array

The below example demonstrates how we can find all indexes of an element in an array in C++.

C++

// C++ Program to illustrate how to find all indexes of a
// specific element in an array
#include <iostream>
using namespace std;

int main()
{
    // Initializing an array with multiple occurrences of
    // some elements
    int myArray[] = { 1, 2, 2, 3, 3, 3, 4, 4, 4, 4 };
    int n = sizeof(myArray) / sizeof(myArray[0]);

    // element to find
    int target = 3;

    cout << "The element " << target
         << " occurred at indices: ";

    // Iterate through the array
    for (int index = 0; index < n; ++index) {
        if (myArray[index] == target) {
            // If the element matches the search element,
            // print the index
            cout << index << " ";
        }
    }

    return 0;
}

Output

The element 3 occurred at indices: 3 4 5 

Time Complexity: O(n), here n is the size of the array.
Auxilliary Space: O(1)