painfully written quicksort

#include <iostream>
#include <vector>
using namespace std;

void swap(vector<int> &a, int e1, int e2)
{
    int tmp = a[e1];
    a[e1] = a[e2];
    a[e2] = tmp;
}

void pvec(vector<int> &v)
{
    for (int i = 0; i < v.size(); i++)
        cout << v[i] << " ";
    cout << endl;
}

int partition(vector<int> &a, int p, int l, int r)
{
    // move pivot to the right
    swap(a, p, r);

    p = r;
    int P = a[p];

    int sidx = l;

    for (int i = l; i < r; i++)
    {
        if (a[i] < P) {
            swap(a, sidx, i);
            sidx++;
        }
    }

    swap(a, r, sidx);
    return sidx;
}

void quick_sort(vector<int> &a, int l, int r)
{
    if (l >= r)
        return;

    int pind = partition (a, l, l, r);

    quick_sort(a, l, pind-1);
    quick_sort(a, pind+1, r);
}

int main()
{
    int arr[9] = {11, 7, 4, 1, 14, 31, 9, 5, 24};
    vector<int> vec (arr, arr + sizeof(arr) / sizeof(arr[0]) );

    quick_sort(vec, 0, vec.size() - 1);
    pvec(vec);
}