/* Program to convert Fahrenheit degrees to Celsius.
   Requests values until -999 entered.
*/

#include <stdio.h>
#include <math.h>

main () {
    float F, C;         /* Fahrenheit & Celsius */
    printf("Enter Fahrenheit (-999 to stop): ");
    scanf("%f", &F);

    /* Note: the following line compares the float F with -999.  This is
       OK, but floats should not be compared for exact (in)equality with
       fractional or very large numbers, because of rounding errors - see
       text chapter 16.
    */
    while (F != -999) {
        C = 5. * (F - 32.) / 9.;
        printf(
            "    Celsius is %.0f\nEnter Fahrenheit (-999 to stop): ",
            C
        );
        scanf("%f", &F);
    }
}