Figure 15.1  Comparison of C and C++ Control Structures 

/*
 *  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%3c%9.4f    Unsafe\n", day, ' ', radiation_lev);
      else
         printf("  %3d%3c%9.4f    Safe\n", day, ' ', radiation_lev);
      day += 3;
   }

   return (day);
}