/* PrimeNumber.c - A program to accept a number from the user and determine
 * if the number is a prime number. It will then output the correct answer,
 * hopefully, or warn the user they have made an error input.
 *
 * Author: Bill Kirby <wjkirby@gmail.com>
 * Written: January 31, 2006
 *
 */

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

#define ULONG unsigned long int

int main(void)
{
	/****** Variable declarations ******/
	
	ULONG usersNumber = 0;		// Users input
	int evenCheck = 0;		// Check for even number
	int flag = 0;			// Flag for found prime number
	int primeCheck = 0;		// Check for prime number
	ULONG i = 0;			// Counter for loop
	
	/****** Print instructions ******/
	
	printf("\n\nThis program will determine if a number is a prime number.\n");
	printf("Enter a positive integer number from 1 to 4294967295 or enter a zero to exit.\n\n");

	/********************************************
	 *      Check for Prime Number Routine
	 ********************************************/
	
	do
	{
		printf("Enter a positive integer number: ");
		scanf("%u", &usersNumber);

	/********************************************************************************************
	 * This section is commented out because I can't get it to work due to the unsigned 
	 * integer variable I'm using for the users input. I'll have to learn how to error check
	 * for this type of situation.
	 *
			       
		if(usersNumber < 0)
		{
			printf("You entered a negative number, try again.\n");
		}
		else
		{
 	 *********************************************************************************************/

		
			/* Determine if the number is even or odd. If odd check for prime numbers */
			
			evenCheck = (usersNumber % 2);
			if(evenCheck == 0 && usersNumber != 0)
				printf("The number %u is an even number and can not be " \
						"a prime number.\n", usersNumber);
			else
			{
				if(usersNumber == 0)
					break;
				else
				{
					for(i=3; i <= (usersNumber-1); i++)
					{
						primeCheck = (usersNumber % i);
						if(primeCheck == 0)
						{
							printf("The number %u is divisible by %u.\n", \
									usersNumber, i);
							flag = 1;
						}
					}
				}
				if(flag == 0 && usersNumber != 0)
					printf("UREAKA! %u is a prime number!\n", usersNumber);
			}
			
//		}		// This bracket goes with the commented out section above
		
		if(flag == 1)
			printf("The number %u is not a prime number, try again.\n", usersNumber);
		
		flag = 0;	// Reset flags for next loop thru
		evenCheck = 0;
		primeCheck = 0;

		printf("\n");	// Make a little breathing room
	}
	while(usersNumber != 0);

	if(usersNumber == 0)
		printf("Thanks for playing! Goodbye!\n\n");

	exit(0);
}