Exercise 3.3 Calculate a discounted price

Exercise 3-3. Write a program that will calculate the price for a quantity entered from
the keyboard, given that the unit price is $5 and there is a discount of 10 percent for
quantities over 30 and a 15 percent discount for quantities over 50.

// Exercise 3.3 Calculate a discounted price

// I interpreted this exercise as implying that the 10% applies to items 31 to 50
// and the 15% applies to items in excess of 50.
// That is, you don't get 15% discount on the whole price when you order 51 items.

// There is more than one way of doing this so different is not necessarily wrong.

#include <stdio.h>

int main(void)
{
  const int level1 = 30;               // Quantity over this level are at discount1
  const int level2 = 50;               // Quantity over this level are at discount2
  const double discount1 = 0.10;       // 10% discount
  const double discount2 = 0.15;       // 15% discount
  const double unit_price = 5.0;       // Basic unit price
  int quantity = 0;
  int qty_full_price = 0;              // 0 to 30 at full price
  int qty_level1 = 0;                  // 31 to 50 at level1 price
  int qty_level2 = 0;                  // Over 50 at level2 price
  printf("Enter the quantity that you require: ");
  scanf("%d", &quantity);
 
  if(quantity > 50)                     // Quantity over 50
  {
    qty_full_price = level1;
    qty_level1 = level2 - level1;
    qty_level2 = quantity - level2;
  }
  else if(quantity > 30)                // Quantity is from 30 to 50
  {
    qty_full_price = level1;
    qty_level1 = quantity - level1;
  }
  else
    qty_full_price = quantity;

  printf("The total price for %d items is $%.2lf
", quantity,
    unit_price*(qty_full_price + (1.0 - discount1)*qty_level1 + (1.0 - discount2)*qty_level2));
  return 0;
}