Exercise 14.13: Adding substraction and compound substraction

ch14/README.md

@@ -119,7 +119,8 @@ see [Exercise 14.5](#exercise-145)
 ## Exercise 14.13:
 >Which other arithmetic operators (Table 4.1 (p. 139)), if any, do you think Sales_data ought to support? Define any you think the class should include.
 
-no others.
+Substraction, in order to be able to revert a previously addition.
+[hpp](ex14_13.h) | [cpp](ex14_13.cpp) | [Test](ex14_13_TEST.cpp)
 
 ## Exercise 14.14:
 >Why do you think it is more efficient to define `operator+` to call `operator+=` rather than the other way around?

ch14/ex14_13.cpp

@@ -0,0 +1,62 @@
+//
+//  ex14_13.cpp
+//  Exercise 14.13
+//
+//  Created by pezy on 3/9/15.
+//  Substraction and compound-substraction operations added by hoeselm on 4/10/16.
+//
+//  @Brief implementation of class Sales_data
+//  @See ex14_13.h
+
+#include "ex14_13.h"
+
+Sales_data::Sales_data(std::istream &is) : Sales_data()
+{
+    is >> *this;
+}
+
+Sales_data& Sales_data::operator+=(const Sales_data &rhs)
+{
+    units_sold += rhs.units_sold;
+    revenue += rhs.revenue;
+    return *this;
+}
+
+
+Sales_data& Sales_data::operator-=(const Sales_data &rhs)
+{
+    units_sold -= rhs.units_sold;
+    revenue -= rhs.revenue;
+    return *this;
+}
+
+std::istream& operator>>(std::istream &is, Sales_data &item)
+{
+    double price = 0.0;
+    is >> item.bookNo >> item.units_sold >> price;
+    if (is)
+        item.revenue = price * item.units_sold;
+    else
+        item = Sales_data();
+    return is;
+}
+
+std::ostream& operator<<(std::ostream &os, const Sales_data &item)
+{
+    os << item.isbn() << " " << item.units_sold << " " << item.revenue << " " << item.avg_price();
+    return os;
+}
+
+Sales_data operator+(const Sales_data &lhs, const Sales_data &rhs)
+{
+    Sales_data sum = lhs;
+    sum += rhs;
+    return sum;
+}
+
+Sales_data operator-(const Sales_data &lhs, const Sales_data &rhs)
+{
+    Sales_data sum = lhs;
+    sum -= rhs;
+    return sum;
+}

ch14/ex14_13.h

@@ -0,0 +1,51 @@
+//
+//  ex14_13.h
+//  Exercise 14.13
+//
+//  Created by pezy on 3/9/15.
+//  Substraction and compound-substraction operations added by hoeselm on 4/10/16.
+//
+//  @See ex7_41.h
+//  @Add overloaded input, output, addition, and compound-assignment operators
+
+#ifndef CP5_CH14_EX14_13_H
+#define CP5_CH14_EX14_13_H
+
+#include <string>
+#include <iostream>
+
+class Sales_data {
+    friend std::istream& operator>>(std::istream&, Sales_data&); // input
+    friend std::ostream& operator<<(std::ostream&, const Sales_data&); // output
+    friend Sales_data operator+(const Sales_data&, const Sales_data&); // addition
+    friend Sales_data operator-(const Sales_data&, const Sales_data&); // substraction
+
+public:
+    Sales_data(const std::string &s, unsigned n, double p):bookNo(s), units_sold(n), revenue(n*p){ }
+    Sales_data() : Sales_data("", 0, 0.0f){ }
+    Sales_data(const std::string &s) : Sales_data(s, 0, 0.0f){ }
+    Sales_data(std::istream &is);
+
+    Sales_data& operator+=(const Sales_data&); // compound-assignment
+    Sales_data& operator-=(const Sales_data&); // compound-substraction
+    std::string isbn() const { return bookNo; }
+
+private:
+    inline double avg_price() const;
+
+    std::string bookNo;
+    unsigned units_sold = 0;
+    double revenue = 0.0;
+};
+
+std::istream& operator>>(std::istream&, Sales_data&);
+std::ostream& operator<<(std::ostream&, const Sales_data&);
+Sales_data operator+(const Sales_data&, const Sales_data&);
+Sales_data operator-(const Sales_data&, const Sales_data&);
+
+inline double Sales_data::avg_price() const
+{
+    return units_sold ? revenue/units_sold : 0;
+}
+
+#endif // CP5_CH14_EX14_13_H

ch14/ex14_13_TEST.cpp

@@ -0,0 +1,25 @@
+#include "ex14_13.h"
+
+int main()
+{
+  Sales_data s1("book1", 150, 10);
+  Sales_data s2("book1", 200, 20);
+
+  std::cout << s1 << std::endl;
+
+  // Assignment
+  s1 = s1 + s2;
+  std::cout << s1 << std::endl;
+
+  // Compound assignment
+  s1 += s2;
+  std::cout << s1 << std::endl;
+
+  // Compound substraction
+  s1 -= s2;
+  std::cout << s1 << std::endl;
+
+  // Substraction
+  s1 = s1 - s2;
+  std::cout << s1 << std::endl;
+}