/* A program to test consistency-checking of user inputs.  Asks for
a non-negative mass, and repeatedly complains until it gets one.
Then it prints the final value back out again as a check. */

#include <stdio.h>

main () {
    float mass_in_kilos;
    /* Ask the user for a non-negative mass in kilograms. */
    printf("What is the mass in kilograms? ");

    /* Input the answer. */
    scanf("%f", &mass_in_kilos);

    /* while the answer is negative: */
    while (mass_in_kilos < 0.0) {
        /* Explain the error and ask for another value. */
        printf("Sorry, masses cannot be negative.  Please re-enter: ");

        /* Input another mass value. */
        scanf("%f", &mass_in_kilos);
    }
    /* Print the mass back as a check. */
    printf("The mass is %f kg.\n", mass_in_kilos);
}