Figure 5.16  Program to Compute Radiation Levels
/*
 * Calculates and displays a table showing the safety level of a coffee room.
 */

#include <stdio.h>

#define SAFE_RAD     0.466  /* safe level of radiation	*/
#define SAFETY_FACT  10.0   /* safety factor 	*/

int rad_table(double init_radiation, double min_radiation);

int
main(void)
{

      int    day;            /* day user can enter room 	*/
      double init_radiation, /* radiation level right after leak 	*/
	     min_radiation;  /* safe level divided by safety factor	*/

      /* Compute stopping level of radiation.	*/
      min_radiation = SAFE_RAD / SAFETY_FACT;

      /* Prompts user to enter initial radiation level 	*/
      printf("Enter the radiation level (in millirems)> ");
      scanf("%lf", &init_radiation);

      /* Displays table	*/
      day = rad_table(init_radiation, min_radiation);

      /* Display day the user can enter the room.	*/
      printf ("\nYou can enter the room on day %d.\n", day);

      return (0);
}

/*
 * Displays a table showing the radiation level and safety status every 3
 * days until the room is deemed safe to enter. Returns the day number for
 * the first safe day.
 * Pre : min_radiation and init_radiation are defined.
 * Post: radiation_lev <= min_radiation
 */
int
rad_table(double init_radiation, double min_radiation)
{
      int    day;              /* days elapsed since substance leak 	*/
      double radiation_lev;    /* current radiation level	*/

      day = 0;
      printf("\n   Day   Radiation   Status\n        (millirems)\n");
      for  (radiation_lev = init_radiation;
	    radiation_lev > min_radiation;
	    radiation_lev /= 2.0) {
         if  (radiation_lev > SAFE_RAD)
                printf("  %3d%5c%9.4f   Unsafe\n", day, ' ', radiation_lev);
         else
                printf("  %3d%5c%9.4f   Safe\n", day, ' ', radiation_lev);
         day += 3;
      }

      return (day);
}


Enter the radiation level (in millirems)> 150.0

   Day    Radiation   Status
         (millirems)
    0	150.0000 	Unsafe
    3 	75.0000 	Unsafe
    6 	37.5000	Unsafe
    9	18.7500	Unsafe
   12	9.3750	Unsafe
   15	4.6875	Unsafe
   18	2.3438	Unsafe
   21	1.1719	Unsafe
   24	0.5859	Unsafe
   27	0.2930	Safe
   30	0.1465	Safe
   33	0.0732	Safe

You can enter the room on day 36.