Program to find the smallest element missing in a sorted array in C++

#include<iostream>
#include<algorithm>

using namespace std;

int smallest_missing(int arr[], int start, int end) {
  if (start > end) {
    return end + 1;
  }

  if (start != arr[start]) {
    return start;
  }

  int mid = (start + end) / 2;

  if (arr[mid] == mid) {
    return smallest_missing(arr, mid + 1, end);
  }

  return smallest_missing(arr, start, mid);
}

int main() {
  int arr[100], n, i;
  cout << "Enter number of elements: ";
  cin >> n;
  cout << "\nEnter elements: ";

  for (i = 0; i < n; i++) {
    cin >> arr[i];
  }

  cout << "Original array: ";

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

  int answer;

  answer = smallest_missing(arr, 0, n - 1);

  cout << "\nSmallest missing element is " << answer;

  return 0;
}

Output

Enter number of elements: 5

Enter elements: 1 2 3 5 6
Original array: 1 2 3 5 6
Smallest missing element is 4