ex4_11.cpp

Beginning Visual C++ 6源码。Wrox。

// EX4_11.CPP
// Calculating primes using dynamic memory allocation
#include <iostream>
#include <iomanip>
#include <cstdlib>
using namespace std;

int main()
{
   long* pprime=0;                // Pointer to prime array
   long trial = 5;                // Candidate prime
   int count = 3;                 // Count of primes found
   int found = 0;                 // Indicates when a prime is found
   int max = 0;                   // Number of primes required

   cout << endl
        << "Enter the number of primes you would like: ";
   cin >> max;                    // Number of primes required

   if(!(pprime=new long[max]))
   {
      cout << endl
           << "Memory allocation failed.";
      exit(1);                   // Terminate program
   }

   *pprime = 2;                  // Insert three
   *(pprime+1) = 3;              // seed primes
   *(pprime+2) = 5;

   do
   {
      trial += 2;                         // Next value for checking
      found = 0;                          // Set found indicator
      for(int i = 0; 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 == 0)                     // We got one...
         *(pprime+count++) = trial;       // ...so save it in primes array
   } while(count < max);

   // Output primes 5 to a line
   for(int i = 0; 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
   cout << endl;
   return 0;
}