#include <iostream.h>
#include <math.h>
#include <fstream.h>


/*Author: Carl Staab
	Last modified: October 28, 2000
	Description: It's a prime number tester.  What else?
	Writes to file primenum.txt
	I'm not sure what'll happen if you start/end on a prime- so just
	start/end on 1 or an even number.
I just made the obvious improvement that if a num has any factors, we can break the loop
and to start at 2 instead of (n^.5) - 1*/

void factortester(int start, int finish, ofstream a);

void main()
{
	int start, finish;
	ofstream a;
	a.open("primenum.txt");

	cout << "Prime Number Tester\n\n";
	cout << "Enter the (positive) number to start testing at ";
	cin >> start;
	cout << "Enter the (higher) number to finish testing at  ";
	cin >> finish;
	factortester(start, finish, a);
	a.close();
	return;
}

void factortester(int start, int finish, ofstream a)
{
	int count, count_two, factor_exist = 0, num_prime = 0, flr;
	

	for (count = start; count <= finish; count++)
	{
		flr = floor(sqrt(count));
		for (count_two = 1; (count_two <= flr && factor_exist < 2); count_two++)
		{
			if (count % count_two == 0)
				factor_exist++;
		}
	
	if (factor_exist <= 1)
	{
		a << count << endl;
		num_prime++;
	}

	factor_exist = 0;
	}

	cout << "There were " << num_prime << " prime numbers.";
	return;
}