How to calculate Tamilnadu Electronic Bill in C Program

Program:
#include<stdio.h>
#include<conio.h>
#include<math.h>

void main()
{
float r=0.0,a=1.1,b=1.8,c=3.5,d=5.75;
clrscr();
printf("Enter the readings\n");
scanf("%f",&r);
if(r<=100)
printf("Rupees=%f",r*a);
else if((r>100)&&(r<=200))
printf("Rupees=%f",r*b);
else if((r>200)&&(r<=500))
printf("Rupees=%f",r*c);
else if(r>500)
printf("Rupees=%f",r*d);
getch();
}