C++ Merge Sort

gistfile1.cpp

#include <iostream>
#include <stdlib.h>

/*
This implementation could be improved using
sentinels.
*/


void merge_sort(int *list, int p, int r);
void merge(int *list, int p, int q, int r);

int main(int argc, char const *argv[])
{
	int n = 25;
    int list[n];
    srand(time(NULL));

    std::cout << "Before sorting" << std::endl;
    for (int i = 0; i < n; i++)
    {
        list[i] = rand() % 300;
        std::cout << list[i] << ", ";
    }
    std::cout << std::endl;
    
    merge_sort(list, 0, n - 1);

    std::cout << "After sorting" << std::endl;
    for (int j = 0; j < n; j++)
    {
        std::cout << list[j] << ", ";
    }
    std::cout << std::endl;

	return 0;
}

void merge_sort(int *list, int p, int r)
{
	if (p < r)
	{
		int q = (p + r) / 2;
		merge_sort(list, p, q);
		merge_sort(list, q + 1, r);
		merge(list, p, q, r);
	}
}

void merge(int *list, int p, int q, int r)
{
	int length = r - p + 1;
	int i = p, j = p, k = q + 1;
	int aux_list[length + p];
	std::copy(list, list + length + p , aux_list);
	while (j <= q && k <= r)
	{
		if (aux_list[j] < aux_list[k])
		{
			list[i] = aux_list[j];
			j++;
		}
		else
		{
			list[i] = aux_list[k];
			k++;
		}
		i++;
	}
	while (j <= q)
	{
		list[i] = aux_list[j];
		j++;
		i++;
	}
	while (k <= r)
	{
		list[i] = aux_list[k];
		k++;
		i++;
	}
}