SieveOfEratosthenes

//
//  main.cpp
//  C6
//
//  Created by Betsalel Williamson on 10/1/11.
//  Chapter 6:
//  Research and implement the Sieve of Eratosthenes.

#include <stdio.h>
#include <stdlib.h>

static int* getSieveOfEratosthenes(int arraySize) {

   /* taken from calloc example  on http://www.cplusplus.com/reference/clibrary/cstdlib/calloc/ */
   int* pData;
   pData = (int*) calloc (arraySize,sizeof(int));
   if (pData==NULL) exit (1);

   //fill our new array with numbers
   int counter, currentNumber;

   for (counter = 0; counter < arraySize; counter++) {
      pData[counter]=counter;
   }

   printf ("Primes up to %d\n\n", arraySize);

   for (counter = 0; counter < arraySize; counter++) {
      currentNumber = counter;//a way to keep the position in the counting line

      //prime number logic starts with numbers greater than 1
      if (counter > 1) {
         for (counter*=2; counter < arraySize; counter+=currentNumber) {//we start with the number times two, as long as its less than the full amount, increment it with the current number

            pData[counter]=0;//sets non prime to zero
         }
      } else {//accounts for the numbers less than 2
         pData[counter]=0;
      }

      //set the counter back to the current number after misusing the counter variable
      counter = currentNumber;
   }

   return pData;
}

static int countNonZeros(int *array, int arraySize) {

   int primeCounter = 0, counter;

   for (counter = 0; counter < arraySize; counter++) {
      if (array[counter]>0) {
         primeCounter++;
      }
   }

   return primeCounter;
}

static int countArray(int *array, int arraySize) {

   int primeCounter = 0, counter;

   for (counter = 0; counter < arraySize; counter++) {
//      printf("%x\n", counter);
      if (array[counter]>0) {
         primeCounter++;
      }
   }

   return primeCounter;
}

//display prime numbers
static void printArray(int* array, int arraySize, int whenToSlashN) {

   for (int counter = 0; counter < arraySize; counter++) {
      printf ("%3d ",array[counter]);
      if ((counter+1)%whenToSlashN == 0) {//counter + 1 is there so you start counting at 1 not 0.
         printf("\n");
      }
   }
}

static int *stripZerosFromArray(int* array, int arraySize) {

   int* newArray;
   int counter = 0, currentNumber = 0;

   newArray = (int*) calloc (arraySize,sizeof(int));
   if (newArray==NULL) exit (1);

   for (counter=0; counter<arraySize; counter++) {
      if (array[counter] > 0) {
         newArray[currentNumber++] = array[counter];
      }
   }

   //free old array after removing the zeros.
   free(array);
   return newArray;
}

int main (int argc, const char * argv[])
{
   int arraySize = 0;
   int* primeNumbers;

   printf ("Enter the limit: ");
   scanf ("%d",&arraySize);

   primeNumbers = getSieveOfEratosthenes(arraySize);

   primeNumbers = stripZerosFromArray(primeNumbers, arraySize);
   arraySize = countArray(primeNumbers, arraySize);

//   printf("%d", arraySize);

   printArray(primeNumbers, countArray(primeNumbers, arraySize), 11);

   printf("\n\nNumber of primes: %d\n", countNonZeros(primeNumbers, arraySize));

   printf("\n\n");

//system("pause");

   //freeing the array created with getSieveOfEratosthenes
   free(primeNumbers);

   return EXIT_SUCCESS;
}