#include <iostream>
#include <fstream>
#include <string>
using namespace std;

	int fPrime(int);

	//Exercise 22
	int main(){
		char repeat = 'y';
		while (repeat == 'y' || repeat == 'Y'){
			int usrIn;
			cout << "\nEnter number to check if it is prime:";
			cin >> usrIn;

			if (fPrime(usrIn) == 0) //remainder 0 = NOT prime
				cout << "\nNumber " << usrIn << " is NOT a PRIME.\n\n";
			else //non-prime
				cout << "\nNumber " << usrIn << " is PRIME\n\n";

			cout << "Enter (y|Y) to check another number: ";
			cin >> repeat;
		}
		cout << "\nPress enter for problem 23, 100 prime output" << endl;
		cin.get();
		cin.ignore();

		//File Block (Exercise 23)
		ofstream outFile;
		string xFile = "1-100_Primes.txt";
		outFile.open(xFile);
		outFile.clear();
		//Find prime and write to file if remainder not 0 (prime)
		for (int x = 1; x <= 100; x++){			
			if (fPrime(x) != 0){
				outFile << x << "\n";
			}
		}
		outFile.close();
		cout << "Output 1-100 primes to: " << xFile << "\n\n";
		system("pause");
		cout << endl;
		return 0;
	}

	//Check prime and return single value
	int fPrime(int funcNr){
		int yo;
		if (funcNr == 2) //2 is a prime, using as divider
			return 1;
		else if (funcNr < 2) //no primes below 2
			return 0;
		else{
			for (int ctr = 2; ctr < funcNr; ctr++){ // 2 is first divider over 1				
				if (funcNr % ctr == 0)
					return 0;
				yo = (funcNr % ctr);
			}
		}
		return yo;
	}