Binary search, recursive

// Binary search, recursive.

#include <iostream>
using namespace std;

// Find a number in a list.
int find_number(int number_list[], int number_to_find,
    int range_start, int range_end)
{
    int index_of_found_number = 0;
    int range_middle; // This is the current middle of the range.

    // If we have searched all the sections,
    if (range_start > range_end) {

        index_of_found_number = -1; // The number is not on the list.

    }
    // If there is more to search,
    else {

        // Find the middle of the range.
        range_middle = (range_start + range_end) / 2;

        // If the middle number is equal to the number we're looking for,
        if (number_list[range_middle] == number_to_find) {

            // It was found in the middle.
            index_of_found_number = range_middle;
        }
        // If the middle number is greater than the number we're looking for,
        else if (number_list[range_middle] > number_to_find) {

            // Search the range before the middle number.
            index_of_found_number = find_number(number_list, number_to_find,
                range_start, range_middle - 1);
        }
        // If the middle number is less than the number we're looking for,
        else {

            // Search the range after the middle number.
            index_of_found_number = find_number(number_list, number_to_find,
                range_middle + 1, range_end);
        }
    }

    return index_of_found_number;
}

int main()
{
    // List of numbers to search.
    int numbers[] = {2, 4, 6, 7, 9, 10, 14, 15, 17, 19, 26, 29};

    // Calculate the number of elements in the array.
    int num_elements = sizeof(numbers) / sizeof(int);
    int input = 0; // The number to look for.
    int index = 0; // Index of found number.

    cout << "What number would you like to find? ";
    cin >> input; // Get the number we are searching for.
    // Search for the number.
    index = find_number(numbers, input, 0, num_elements - 1);

    // If if the number was not found.
    if (index == -1) cout << "The number " << input
        << " is not on the list.\n";

    // Otherwise, if the number was found, display the
    // index where it was found
    else cout << "The number " << input << " is located at index "
        << index << '\n';

    // End the program.
    return 0;
}