Quick Sort

#include <iostream>
#include <conio.h>
#include <iomanip>

using namespace std;

void Quick_Sort(int *a, int left, int right)
{
        if (left<right)
        {
            int i = left;
            int j = right;
            int k = (left+right)/2;
            int t = a[k];
            while (i<=j)
            {
                while (a[i]<t) i=i+1;
                while (a[j]>t) j=j-1;
                if (i <= j)
                {
                    int tg = a[i];
                    a[i] = a[j];
                    a[j] = tg;
                    i++; j--;
                }
            }
            Quick_Sort(a,left,j);   // j la right
            Quick_Sort(a,i,right);  // i la left
        }
}


void in(int n, int *p)
{
    for (int i=0; i<n; i++)
    cout << setw(6) << p[i];
}

main()
{
    int n;
    int i,j;
    int m, k, t, tg;
    int *a;
    do {
        cout << "Nhap n: "; cin >> n;
    }while (n<=0);

    a = new int[n];

    for (i=0; i<n; i++)
    {
        cout << "Nhap a[" << i+1 << "]: ";
        cin >> a[i];
    }

    cout << "Day da nhap: " << endl;
    in(n,a);

    //sx
    /*
    for (i=0; i<n; i++)
    {
        j = i;
        m = a[i+1];
        while(j>-1 && a[j]>m)
        {
            a[j+1]=a[j];
            --j;
        }
        a[j+1] = m;
    }
    */

    /*
    for (i=0; i<n-1; i++)
    for (j=n-1; j>i; j--)
    {
        if (a[j] < a[j-1]) {
            tg = a[j];
            a[j] = a[j-1];
            a[j-1] = tg;
        }
    }
    */
    /*
    for (i=0; i<n-1; i++)
    {
        m = i;
        for (j=i+1; j<n; j++)
        if (a[j]<a[m]) m=j;
        if (i!=m)
        {tg = a[i]; a[i]= a[m]; a[m]=tg;}
    }

    */
    Quick_Sort(a,0,n-1);


    cout << endl << "Day da sx: " << endl;
    in(n,a);
    getch();
}