Calculating primes using pointer notation - C++ Data Type

C++ examples for Data Type:Pointer

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Description

Calculating primes using pointer notation

Demo Code

#include <iostream>
#include <iomanip>

int main()/*from   w ww  .  j  ava  2s .  co  m*/
{
  const int max {100};              // Number of primes required
  long primes[max] {2L, 3L, 5L};       // First three primes defined
  int count {3};                    // Count of primes found so far
  long trial {5};                      // Candidate prime
  bool isprime {true};                 // Indicates when a prime is found

  do
  {
    trial += 2;                        // Next value for checking
    int i {};                       // Index to primes array

    // Try dividing the candidate  by all the primes we have
    do
    {
      isprime = trial % *(primes + i) > 0;  // False for exact division
    } while (++i < count && isprime);

    if (isprime)
    {                                  // We got one...
      *(primes + count++) = trial;     // ...so save it in primes array
    }
  } while (count < max);
  // Output primes 10 to a line
  std::cout << "The first " << max << " primes are:" << std::endl;
  for (int i{} ; i < max ; ++i)
  {
    std::cout << std::setw(7) << *(primes + i);
    if ((i+1) % 10 == 0)               // Newline after every 10th prime
      std::cout << std::endl;
  }
  std::cout << std::endl;
}

Result


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