C++ "Sắp xếp Bubble + Swap"

#include <iostream>
using namespace std;

void swap (int *a, int i, int j){
    int temp = a[i]; // a[i] = *(a + 1)
    a[i] = a[j];
    a[j] = temp;
}

void bubble_sort(int *a, int n){
    for (int i = 0; i < n -1; i++){
        for (int j = i + 1; j < n; j++){
            if (a[i] < a[j])
            swap (a, i ,j);
        }
    }
}

int main(){
    int n, *a, tg;
    do{
        cout << "Nhap n vao ";
        cin >> n;
        if (n < 0)
            cout << "Phai nhap n > 0!" << endl;
    } while (n <= 0);

    a = new int[n];

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

    }


    bubble_sort(a, n);


    for (int i = 0; i < n; i++){
        cout << a[i] << " ";
        }

    delete[] a;
    return 0;
}