C++ Program to Find Index of First Occurrence of a Value in Array

In C++, an array is a data structure that stores elements of the same type in contiguous memory locations. In this article, we will learn how to find the index of the first occurrence of a specific value in an array in C++.

Example:

Input: 
int arr[] = {5, 7, 1, 2, 3, 7, 1} 
Target = 1

Output: 
The first occurrence of 1 is at index: 2

Finding the Index of the First Occurrence of an Element in an Array

To find the index of the first occurrence of a value in an array, we can simply use a loop to iterate through the array and check if the element matches with the target if it matches return the index that is the first occurrence of a value in an array.

C++ Program to Find the Index of the First Occurrence of a Value in an Array 

The below example demonstrates the use of a for loop to find the index of the first occurrence of a value in a given array in C++.

C++

// C++ Program to show how to Find the Index of the First Occurrence of
// a Value in an Array
#include <iostream>
using namespace std;

int main()
{
    // initializing array
    int arr[] = { 5, 7, 1, 2, 3, 7, 1 };
    int n = sizeof(arr) / sizeof(arr[0]);
    // target whose first occurence need to be searched
    int target = 1;
    int index = -1;

    // using a for loop to find the first occurrence of
    // the element in the array.
    for (int i = 0; i < n; i++) {
        if (arr[i] == target) {
            index = i;
            break;
        }
    }

    // if target is found print it's index
    if (index != -1) {
        cout << "The first occurrence of " << target
             << " is at index: " << index << endl;
    }
    // else element not found
    else {
        cout << "Element not found." << endl;
    }

    return 0;
}

Output

The first occurrence of 1 is at index: 2

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