Water BIll

  #include <stdio.h>

  #define DEMAND_CHG  35.00    /* basic water demand charge                     */
  #define PER_1000_CHG 1.10    /* charge per thousand gallons used              */
  #define LATE_CHG     2.00   /* surcharge assessed on unpaid balance          */
  /* Function prototypes                                                       */
  void instruct_water(void);
  double comp_use_charge(int previous, int current);
  double comp_late_charge(double unpaid);
  void display_bill(double late_charge, double bill, double unpaid);
  double getdataunpaid(void);
  int getdataprevious(void);
  int getdatacurrent(void);
  double figurebill(double,double,double);

  int
  main(void)
  {
          int    previous;    /* input - meter reading from previous quarter
                                 in thousands of gallons                    */
          int    current;     /* input - meter reading from current quarter */
          double unpaid;      /* input - unpaid balance of previous bill    */
          double bill;        /* output - water bill                        */
          int    used;        /* thousands of gallons used this quarter     */
          double use_charge;  /* charge for actual water use                */
          double late_charge; /* charge for nonpayment of part of previous
                                 balance                                    */
          /* Display user instructions.                                     */
          instruct_water();
          /* Get data: unpaid balance, previous and current meter
             readings.*/
            unpaid= getdataunpaid();
            previous=getdataprevious();
            current=getdatacurrent();
          /* Compute use charge.                                            */
          use_charge = comp_use_charge(previous, current);
          /* Determine applicable late charge                               */
          late_charge = comp_late_charge(unpaid);
          /* Figure bill.                                                   */
          bill = figurebill(use_charge,unpaid,late_charge);
          /* Print bill.                                                    */
          display_bill(late_charge, bill, unpaid);
          return (0);
  }
  /*
   * Displays user instructions
   */
  void
  instruct_water(void)
  {
        printf("This program figures a water bill ");
        printf("based on the demand charge\n");
        printf("($%.2f) and a $%.2f per 1000 ", DEMAND_CHG, PER_1000_CHG);
        printf("gallons use charge.\n\n");
        printf("A $%.2f surcharge is added to ", LATE_CHG);
        printf("accounts with an unpaid balance.\n");
        printf("\nEnter unpaid balance, previous ");
        printf("and current meter readings\n");
        printf("on separate lines after the prompts.\n");
        printf("Press <return> or <enter> after ");
        printf("typing each number.\n\n");
  }
  /*
   * Computes use charge
   * Pre: previous and current are defined.
   */
  double
  comp_use_charge(int previous, int current)
  {
        int used;          /* gallons of water used (in thousands)             */
        double use_charge; /* charge for actual water use                      */
        used = current - previous;
        use_charge = used * PER_1000_CHG;
        return (use_charge);
  }

  /*
   * Computes late charge.
   * Pre : unpaid is defined.
   */
  double
  comp_late_charge(double unpaid)
  {
        double late_charge; /* charge for nonpayment of part of previous balance  */
        if (unpaid > 0)
              late_charge = LATE_CHG; /* Assess late charge on unpaid balance.    */
        else
              late_charge = 0.0;
        return (late_charge);
  }
  /*
   * Displays late charge if any and bill.
   * Pre : late_charge, bill, and unpaid are defined.
   */
  void
  display_bill(double late_charge, double bill, double unpaid)
     {
         if (late_charge > 0.0) {
               printf("\nBill includes $%.2f late charge", late_charge);
               printf(" on unpaid balance of $%.2f\n", unpaid);
         }
         printf("\nTotal due = $%.2f\n", bill);
  }
  double
  getdataunpaid(){
    double unpaid,previous,current;
     printf("Enter unpaid balance> $");
          scanf("%lf", &unpaid);

          return(unpaid);
  }
  int
  getdataprevious(){
    int previous;

          printf("Enter previous meter reading> ");
          scanf("%d", &previous);
          return(previous);
  }
  int
  getdatacurrent(){
    int current;
      printf("Enter current meter reading> ");
          scanf("%d", &current);
          return(current);
  }
  double figurebill(double X,double Y,double Z){
    return (DEMAND_CHG + X + Y + Z);
  }