Поменять местами 3-ий и 5-ый элементы массива используя указатели

#include <iostream>
 
int main()
{
  const int n = 10;
  int a[n];
  for (int i = 0; i < n; ++i)
  {
    std::cout << "a[" << i << "] = ";
    std::cin >> a[i];
  }
 
  std::cout << "Initial array: ";
  for (int i = 0; i < n; ++i)
    std::cout << a[i];
 
  int * a3 = &a[3];
  int * a5 = &a[5];
  int temp = *a3;
  *a3 = *a5;
  *a5 = temp;
 
  std::cout << "Changed array: ";
  for (int i = 0; i < n; ++i)
    std::cout << a[i];
 
  return 0;
}

#include <iostream>
 
int digit_sum(int x)
{
  int n = 0;
  int digits[10];
  while (x > 0)
  {
    digits[n++] = x % 10;
    x /= 10;
  }
 
  int sum = 0;
  for (int i = 0; i < n; ++i)
  {
    if ((digits[i] != 8) && (digits[i] != 9))
      sum += digits[i];
  }
  return sum;
}
 
int main()
{
  int x = 13579;
  int y = 24680;
 
  std::cout << "x = " << x << ". sum = " << digit_sum(x) << "\n";
  std::cout << "y = " << y << ". sum = " << digit_sum(y) << "\n";
}

int *a3 = a+3;
int *a5 = a+5;

#include <iostream>
 
int main()
{
  int n;
  std::cout << "Enter array size: ";
  std::cin>>n;
  int *a=new int[n];
  for (int* pa=a;pa!=a+n;++pa)
  {
    std::cout << "a[" << i << "] = ";
    std::cin >> *pa;
  }
 
  std::cout << "Initial array: ";
  for (int* pa=a;pa!=a+n;++pa)
      std::cout << *pa<<' ';
  std::cout<<'\n';
 
  int *a3 = a+3;
  int *a5 = a+5;
  int temp = *a3;
  *a3 = *a5;
  *a5 = temp;
 
  std::cout << "New array: ";
  for (int* pa=a;pa!=a+n;++pa)
      std::cout << *pa<<' ';
  std::cout<<'\n';
  delete[] a;
  return 0;
}