/* assert.c -- use assert() */
#include <stdio.h>
#include <math.h>
#include <assert.h>
int main()
{
    double x, y, z;
    
    puts("Enter a pair of numbers (0 0 to quit): ");
    while (scanf("%lf%lf", &x, &y) == 2
           && (x != 0 || y != 0))
    {
        z = x * x - y * y;  /* should be + */
        assert(z >= 0);
        printf("answer is %f\n", sqrt(z));
        puts("Next pair of numbers: ");
    }
    puts("Done");
    
    return 0;
}