qsort

#include <iostream>
#include <cstdio>

#define D_SCL_SECURE_NO_WARNINGS

void swap(int &a, int &b)
{
    int t = a;
    a = b;
    b = t;
}

int partition(int* a, int l, int r)
{
    int i = l - 1;
    for (int j = l; j < r - 1; ++j)
    {
        if (a[j] <= a[r-1])
        {
            i++;
            swap(a[j], a[i]);
        }
    }
    swap(a[i + 1], a[r - 1]);
    return i + 1;
}

void qsort(int *a, int l, int r)
{
    if (l >= r)
        return;
    int q = partition(a, l, r);
    qsort(a, l, q);
    qsort(a, q + 1, r);
}

int main()
{
    int arr[] = { 7, 3, 5, 1, 2 };
    qsort(arr, 0, 5);
    return 0;
}