/**
 * GOLDBACH.C 
 *
 * Exercise solution 2.6.  (C By Dissection Chap. 4, ex. 15)
 *
 * Tests Goldbach's Conjecture on an interval.
 * 26-Feb-03 by Dimon
 **/


/**
 * INCLUDE statements 
 **/
#include "primes.h"


/**
 * DEFINE statements 
 **/
#define BEGIN 0
#define END 1500


/**
 * The main function
 **/
int main(void) {  
  
  /* Declaration of variables */

  int number, firstPrime, lastPrime; 
  int status = 0;


  /* Display program header */
  
  printf("Goldbach's Conjecture:\n");
  printf("Every even integer is a sum of two odd primes.\n");
  printf("----------------------------------------------\n");
  printf("\n");
  printf("Beginning at: %d \n", BEGIN);
  printf("Ending at:    %d \n", END);


  /* A FOR loop calculates and prints out the results */ 

  for(number = BEGIN; number <= END; number++) {
    if (number % 2 == 0) {     /* Only even integers are examined */ 
      firstPrime = 3;
      lastPrime = number - firstPrime;
      /* Repeat until a sum of two odd primes that equals number has
	 been found */
      while ((isPrime(firstPrime) && isPrime(lastPrime)) == 0) {
	firstPrime += 2;
	lastPrime = number - firstPrime;
      } /* WHILE */
      printf("%10d = %9d + %9d \n", number, firstPrime, lastPrime); 
    } /* IF */
  } /* End of FOR loop */

  /* Terminate program */
  return status;    

} /* END OF MAIN */