SP-0301a (exception)

#include "stdafx.h"
#include <iostream>

using namespace std;
double hmean (double a, double b);
int main ()
{
    double x, y, z;
    cout << "Enter two numbers:";
    while (cin >> x >> y)
    {
        z = hmean (x, y);
        cout << "Harmonic mean of " << x << " and " << y << " is " << z << "\n";
        cout << "Enter next set of numbers <q to quit>:";
    }
        cout << "Bye!\n";
        return 0;
}
double hmean ( double a, double b)
{
    if (a == -b)
    {
        cout << "untenable arguments to hmean ()\n";
        abort ();
    }
    return 2.0 * a * b / (a + b);
}