// This program illustrates a sentinel controlled while loop.
// Write a program that calculates the average of an unknown number of positive integers.
// The program is to stop when a negative one (-1) is entered.

#include <iostream>
using namespace std;

int main()
{
	int value, count, sum = 0;

	count = 0;	
	cout << "Please enter positive integers, a -1 to stop" << endl;

	cin >> value;		// initialize

	//test to make sure an invalid number (negative other than -1) was not entered
	while (value < -1)
	{
		cout << " only positive numbers will be used - remember -1 to stop" << endl;
		cin >> value;
	}
	// if positive value add to the sum
	while (value != -1)	// test 
	{
		sum += value;
		count++;		
		cin >> value;	// modify 

		// test for invalid number
		while (value < -1)
	{
		cout << " only positive numbers will be used - remember -1 to stop" << endl;
		cin >> value;
	}
	}

	// calculate average - only if some data to average
	if (count > 0)
		cout << " The average is " << (double)sum / count << endl;
	else
		cout << " No average calculated - no values entered " << endl;

}