// Ex4_11.cpp
// Calculating primes using dynamic memory allocation
#include <iostream>
#include <iomanip>
using std::cin;
using std::cout;
using std::endl;
using std::setw;

int main()
{
  int max {};                                    // Number of primes required
  cout << endl
    << "Enter the number of primes you would like (at least 4): ";
  cin >> max;

  if (max < 4)                                   // Test the user input, if less than 4
    max = 4;                                     // ensure it is at least 4

  // Allocate prime array and initialize with seed primes   
  long* pprime { new long[max] {2L, 3L, 5L} };

  long trial { 5L };                              // Candidate prime
  int count { 3 };                                // Count of primes found
  bool found { false };                           // Indicates when a prime is found


  do
  {
    trial += 2L;                                  // Next value for checking
    found = false;                                // Set found indicator

    for (int i {}; i < count; i++)                // Division by existing primes
    {
      found = (trial % *(pprime + i)) == 0;       // True for exact division
      if (found)                                  // If division is exact
        break;                                    // it's not a prime
    }

    if (!found)                                   // We got one...
      *(pprime + count++) = trial;                // ...so save it in primes array
  } while (count < max);

  // Output primes 5 to a line
  for (int i {}; i < max; i++)
  {
    if (i % 5 == 0)                              // New line on 1st, and every 5th line
      cout << endl;
    cout << setw(10) << *(pprime + i);
  }

  delete[] pprime;                               // Free up memory...
  pprime = nullptr;                              // ...and reset the pointer
  cout << endl;
  return 0;
}