Lowerbound, upperbound when element is existed or non-existed

#include "bits/stdc++.h"
using namespace std;

int lower_bound(int arr[], int n, int X) {
    int l = 0;
    int r = n;

    // Till low is less than high
    while (l < r) {
        int mid = (l+r)/2;

        // If X is less than or equal
        // to arr[mid], then find in
        // left subarray
        if (X <= arr[mid]) {
            r = mid;
        }

        // If X is greater arr[mid]
        // then find in right subarray
        else {
            l = mid + 1;
        }
    }

    // Return the lower_bound index
    return l;
}

int upper_bound(int arr[], int n, int X) {
    int l = 0;
    int r = n;

    // Till low is less than high
    while (l < r) {
        // Find the middle index
        int mid = (l+r)/2;

        // If X is greater than or equal
        // to arr[mid] then find
        // in right subarray
        if (X >= arr[mid]) {
            l = mid + 1;
        }

        // If X is less than arr[mid]
        // then find in left subarray
        else {
            r = mid;
        }
    }

    // Return the upper_bound index
    return l;
}

// Function to implement lower_bound
// and upper_bound of X
void printBound(int arr[], int n, int X) {
    int idx;

    // If lower_bound doesn't exists
    if (lower_bound(arr, n, X) == n) {
        printf("Lower bound doesn't exist");
    }
    else {
        // Find lower_bound
        idx = lower_bound(arr, n, X);
        printf("Lower bound of %d is %d at index % d\n ", X, arr[idx], idx);
    }

    // If upper_bound doesn't exists
    if (upper_bound(arr, n, X) == n) {
        printf("Upper bound doesn't exist");
    }
    else {
        // Find upper_bound
        idx = upper_bound(arr, n, X);
        printf("Upper bound of %d is %d at index % d\n ", X, arr[idx], idx);
    }
}

int main() {
    int arr[] = { 4, 6, 10, 12, 18, 20 };
    int n = sizeof(arr) / sizeof(arr[0]);

    // Element whose lower bound and
    // upper bound to be found
    int X = 6;

    // Function Call
    printBound(arr, n, X);

    printBound(arr, n, 7);
    return 0;
}


/*
eikhane amader r=n newa lage karon output jokhon n asbe tokhon bujhte parobo je array te lowerbound/ upperbound exist kore nah
*/