added 7.41~7.42

ch07/README.md

@@ -243,3 +243,21 @@ private:
   std::string pubdate_;
 };
 ```
+
+## Exercise 7.41 [Header](ex7_41.h)|[Cpp](ex7_41.cpp)|[Test](ex7_41_TEST.cpp)
+## Exercise 7.42
+
+```cpp
+class Book {
+public:
+  Book(unsigned no, std::string name, std::string author, std::string pubdate):no_(no), name_(name), author_(author), pubdate_(pubdate) { }
+  Book() : Book(0, "", "", "") { }
+  Book(std::istream &in) : Book() { in >> no_ >> name_ >> author_ >> pubdate_; }
+
+private:
+  unsigned no_;
+  std::string name_;
+  std::string author_;
+  std::string pubdate_;
+};
+```

ch07/ex7_41.cpp

@@ -0,0 +1,48 @@
+//
+//  ex7_41.cpp
+//  Exercise 7.41
+//
+//  Created by pezy on 11/20/14.
+//  Copyright (c) 2014 pezy. All rights reserved.
+//
+//  @Brief implementation of class Sales_data
+//  @See ex7_41.h
+
+#include "ex7_41.h"
+
+// constructor
+Sales_data::Sales_data(std::istream &is) : Sales_data()
+{
+    std::cout << "Sales_data(istream &is)" << std::endl;
+    read(is, *this);
+}
+
+// member functions.
+Sales_data& Sales_data::combine(const Sales_data& rhs)
+{
+    units_sold += rhs.units_sold;
+    revenue += rhs.revenue;
+    return *this;
+}
+
+// friend functions
+std::istream &read(std::istream &is, Sales_data &item)
+{
+    double price = 0;
+    is >> item.bookNo >> item.units_sold >> price;
+    item.revenue = price * item.units_sold;
+    return is;
+}
+
+std::ostream &print(std::ostream &os, const Sales_data &item)
+{
+    os << item.isbn() << " " << item.units_sold << " " << item.revenue;
+    return os;
+}
+
+Sales_data add(const Sales_data &lhs, const Sales_data &rhs)
+{
+    Sales_data sum = lhs;
+    sum.combine(rhs);
+    return sum;
+}

ch07/ex7_41.h

@@ -0,0 +1,58 @@
+//
+//  ex7_41.h
+//  Exercise 7.41 
+//
+//  Created by pezy on 11/20/14.
+//  Copyright (c) 2014 pezy. All rights reserved.
+//
+//  @See ex7_26.h
+//  @Add 1. use delegating constructors
+//       2. add a statement to the body of each of the constructors that prints a message whether it is executed. 
+
+#ifndef CP5_ex7_41_h
+#define CP5_ex7_41_h
+
+#include <string>
+#include <iostream>
+
+class Sales_data {
+    friend std::istream &read(std::istream &is, Sales_data &item);
+    friend std::ostream &print(std::ostream &os, const Sales_data &item);
+    friend Sales_data add(const Sales_data &lhs, const Sales_data &rhs);
+
+public:
+    Sales_data(const std::string &s, unsigned n, double p):bookNo(s),units_sold(n),revenue(n*p)
+    { std::cout << "Sales_data(const std::string&, unsigned, double)" << std::endl; }
+
+    Sales_data() : Sales_data("", 0, 0.0f)
+    { std::cout << "Sales_data()" << std::endl; }
+
+    Sales_data(const std::string &s) : Sales_data(s, 0, 0.0f)
+    { std::cout << "Sales_data(const std::string&)" << std::endl; }
+
+    Sales_data(std::istream &is);
+
+    std::string isbn() const { return bookNo; };
+    Sales_data& combine(const Sales_data&);
+
+private:
+    inline double avg_price() const;        
+
+private:
+    std::string bookNo;
+    unsigned units_sold = 0;
+    double revenue = 0.0;
+};
+
+inline
+double Sales_data::avg_price() const
+{
+    return units_sold ? revenue/units_sold : 0;
+}
+
+// declarations for nonmember parts of the Sales_data interface.
+std::istream &read(std::istream &is, Sales_data &item);
+std::ostream &print(std::ostream &os, const Sales_data &item);
+Sales_data add(const Sales_data &lhs, const Sales_data &rhs);
+
+#endif

ch07/ex7_41_TEST.cpp

@@ -0,0 +1,55 @@
+//
+//  ex7_41_TEST.cpp
+//  Test of Exercise 7.41
+//
+//  Created by pezy on 11/14/14.
+//  Copyright (c) 2014 pezy. All rights reserved.
+//
+
+#include "ex7_41.h"
+using std::cout; using std::endl;
+
+int main()
+{
+    cout << "1. default way: " << endl;
+    cout << "----------------" << endl;
+    Sales_data s1;   
+
+    cout << "\n2. use std::string as parameter: " << endl;
+    cout << "----------------" << endl;
+    Sales_data s2("CPP-Primer-5th");
+
+    cout << "\n3. complete parameters: " << endl;
+    cout << "----------------" << endl;
+    Sales_data s3("CPP-Primer-5th", 3, 25.8);
+
+    cout << "\n4. use istream as parameter: " << endl;
+    cout << "----------------" << endl;
+    Sales_data s4(std::cin);
+
+    return 0;
+}
+
+// print 
+/*
+ *  1. default way:
+ *  ----------------
+ *  Sales_data(const std::string&, unsigned, double)
+ *  Sales_data()
+ *  
+ *  2. use std::string as parameter:
+ *  ----------------
+ *  Sales_data(const std::string&, unsigned, double)
+ *  Sales_data(const std::string&)
+ *  
+ *  3. complete parameters:
+ *  ----------------
+ *  Sales_data(const std::string&, unsigned, double)
+ *  
+ *  4. use istream as parameter:
+ *  ----------------
+ *  Sales_data(const std::string&, unsigned, double)
+ *  Sales_data()
+ *  Sales_data(istream &is)
+ *
+ */