#include <stdio.h> /* printf */

#define FALSE 0
#define TRUE  1

/**************************************************************************
   Function: is_prime

Description: Takes a number from user/file and checks if it is prime.

     Inputs: number - A number (integer) to be used in prime check
                      process.

    Outputs: Value of either TRUE (integer) or FALSE (integer)
             depending on if the given number is prime or not.
**************************************************************************/
int is_prime(int number)
{
  int i; /*looping variable                           */
  /*holds perceived true or false value (prime or not)*/
  int primeCheck = 0;

  /*checks if number is prime*/
  for(i = 2; i <= (number / 2); ++i)
  {
    if(number % i == 0)
    {
      primeCheck = 1;
      break;
    }
  }

  /*assigns appropriate value to check*/
  if (primeCheck == 0 && number != 1)
  {
    return TRUE;
  }
  else
  {
    return FALSE;
  }
}

/**************************************************************************
   Function: conjecture

Description: Takes 2 numbers that act as a range from user/file and prints
             valid values that match the standard of Goldbach conjecture.

     Inputs: low   - A number (integer) to be used as lower end of range.
             high  - A number (integer) to be used as higher end of range.

    Outputs: Prints the valid values of Goldback conjecture.
**************************************************************************/
void conjecture(int low, int high)
{
  int i;        /*looping variable                     */
  int prime1;   /*holds potential/final first prime(s) */
  int prime2;   /*holds potential/final second prime(s)*/

  for(i = low; i <= high; i++)
  {
    if(i % 2 != 1)
    {
      /*loops through potential first primes*/
      for(prime1 = 2; prime1 < i; ++prime1)
      {
        /*holds 1 or 0 depending on if desired values are found*/
        int found = 0;

        /*breaks if desires values are found*/
        if(found)
        {
          found = 0;
          break;
        }
        /*loops through potential second primes*/
        for(prime2 = 1; prime2 < i; ++prime2)
        {
          /*holds perceived true or false value (prime or not)*/
          int primeCheck1;
          /*holds perceived true or false value (prime or not)*/
          int primeCheck2;

          /*check if potential primes are prime*/
          primeCheck1 = is_prime(prime1);
          primeCheck2 = is_prime(prime2);

          if(primeCheck1 && primeCheck2)
          {
            /*Makes sure values fit standard before printing*/
            if((prime1 <= prime2) && (prime1 + prime2 == i))
            {
              printf("%3i = %3i + %3i\n", i, prime1, prime2);
              found = 1;
              break;
            }

          }
        }
      }
    }
  }
}