cpp/CPrimerPlus6E/Ch07/electric.c

// electric.c -- calculates electric bill 
#include <stdio.h>
#define RATE1   0.13230       // rate for first 360 kwh      
#define RATE2   0.15040       // rate for next 108 kwh  
#define RATE3   0.30025       // rate for next 252 kwh
#define RATE4   0.34025       // rate for over 720 kwh       
#define BREAK1  360.0         // first breakpoint for rates  
#define BREAK2  468.0         // second breakpoint for rates 
#define BREAK3  720.0         // third breakpoint for rates
#define BASE1   (RATE1 * BREAK1)
// cost for 360 kwh            
#define BASE2  (BASE1 + (RATE2 * (BREAK2 - BREAK1)))
// cost for 468 kwh
#define BASE3   (BASE1 + BASE2 + (RATE3 *(BREAK3 - BREAK2)))
//cost for 720 kwh
int main(void)
{
    double kwh;               // kilowatt-hours used         
    double bill;              // charges                     
    
    printf("Please enter the kwh used.\n");
    scanf("%lf", &kwh);       // %lf for type double         
    if (kwh <= BREAK1)
        bill = RATE1 * kwh;
    else if (kwh <= BREAK2)   // kwh between 360 and 468     
        bill = BASE1 + (RATE2 * (kwh - BREAK1));
    else if (kwh <= BREAK3)   // kwh betweent 468 and 720
        bill = BASE2 + (RATE3 * (kwh - BREAK2));
    else                      // kwh above 680               
        bill = BASE3 + (RATE4 * (kwh - BREAK3));
    printf("The charge for %.1f kwh is $%1.2f.\n", kwh, bill);
    
    return 0;
}