update exercises 7.1--7.10

c++ note/chp7/chp7answers.md

@@ -3,4 +3,81 @@ Solutions to Exercises in Chapter Seven
 
 > Exercise 7.1: Write a version of the transaction-processing program from §1.6 (p. 24) using the Sales_data class you defined for the exercises in §2.6.1 (p. 72).
 
-[exercise7_1.cpp](exercise7_1.cpp)
+[exercise7_1.cpp](exercise7_1.cpp)
+
+> Exercise 7.2: Add the combine and isbn members to the Sales_data class you wrote for the exercises in § 2.6.2 (p. 76).
+
+[exercise7_2.h](exercise7_2.h)
+
+> Exercise 7.3: Revise your transaction-processing program from § 7.1.1 (p.256) to use these members.
+
+[exercsie7_3.cpp](exercise7_3.cpp)
+
+> Exercise 7.4: Write a class named Person that represents the name and address of a person. Use a string to hold each of these elements. Subsequent exercises will incrementally add features to this class.
+
+```cpp
+#ifndef EXERCISE7_4_H_
+#define EXERCISE7_4_H_
+
+#include <string>
+using std::string;
+
+struct Person{
+	string name;
+	string address;
+};
+
+#endif
+```
+
+> Exercise 7.5: Provide operations in your Person class to return the name and address. Should these functions be const? Explain your choice.
+
+```cpp
+#ifndef EXERCISE7_4_H_
+#define EXERCISE7_4_H_
+
+#include <string>
+using std::string;
+
+struct Person{
+	string name;
+	string address;
+	string getName() const { return name; }
+	string getAddr() const { return address; }
+};
+
+#endif
+```
+
+These two functions should be `const`. Because these two functions do not modify the object's members, and `const` objects of this class should be able to call these two functions.
+
+> Exercise 7.6: Define your own versions of the add, read, and print functions.
+
+It seems I have done this back in Exercise 7.1.
+
+> Exercise 7.7: Rewrite the transaction-processing program you wrote for the exercises in § 7.1.2 (p. 260) to use these new functions.
+
+It seems I have done this back in Exercise 7.1.
+
+> Exercise 7.8: Why does `read` define its Sales_data parameter as a plain reference and `print` define its parameter as a reference to const?
+
+Because in `read`, the `Sales_data` object will be modified. While in `print`, this function do not modify the object. 
+
+> Exercise 7.9: Add operations to `read` and `print` Person objects to the code you wrote for the exercises in § 7.1.2 (p. 260).
+
+```
+istream& read(istream &is, Person &person){
+	is >> person.name >> person.address;
+	return is;
+}
+
+ostream& print(ostream &os, Person const &person){
+	os << person.name << ' ' << person.address;
+	return os;
+}
+```
+
+> Exercise 7.10: What does the condition in the following if statement do? 
+`if (read(read(cin, data1), data2))`
+
+Take in two objects(data1 and data2) at the same time, and step into the `if` block only when both objects are valid.

c++ note/chp7/exercise7_1.cpp

@@ -14,8 +14,12 @@ struct Sales_data{
 	}
 };
 
-void add(Sales_data one, Sales_data two){
-	one.combine(two);
+Sales_data add(Sales_data const &one, Sales_data const &two){
+	Sales_data res;
+	res.bookNo     = one.bookNo;
+	res.units_sold = one.units_sold + two.units_sold;
+	res.revenue    = one.revenue + two.revenue;
+	return res;
 }
 
 istream& read(istream &is, Sales_data &data){
@@ -25,7 +29,7 @@ istream& read(istream &is, Sales_data &data){
 	return is;
 }
 
-ostream& print(ostream &os, Sales_data const data){
+ostream& print(ostream &os, Sales_data const &data){
 	os << "book number: "   << data.bookNo << endl;
 	os << "units sold: "    << data.units_sold << endl;
 	os << "total revenue: " << data.revenue << endl;

c++ note/chp7/exercise7_2.h

@@ -0,0 +1,44 @@
+#ifndef EXERCISE7_2_H_
+#define EXERCISE7_2_H_
+
+#include <iostream>
+#include <string>
+using namespace std;
+
+struct Sales_data {
+	string bookNo;
+	unsigned units_sold = 0;
+	double revenue = 0.0;
+
+	string isbn() const { return bookNo; }
+	double avg_price() const { return revenue / units_sold; }
+	Sales_data& combine(Sales_data const &data);		//behave same as the `+=` operator, thus return a left-value
+};
+
+Sales_data& Sales_data::combine(Sales_data const &data){
+	units_sold += data.units_sold;
+	revenue    += data.revenue;
+	return *this;
+}
+
+Sales_data add(Sales_data const &one, Sales_data const &two) {
+	Sales_data res = one;
+	return res.combine(two);
+}
+
+istream& read(istream &is, Sales_data &data) {
+	is >> data.bookNo;
+	is >> data.units_sold;
+	is >> data.revenue;
+	return is;
+}
+
+ostream& print(ostream &os, Sales_data const data) {
+	os << "book number: " << data.bookNo << endl;
+	os << "units sold: " << data.units_sold << endl;
+	os << "total revenue: " << data.revenue << endl; 
+	os << "averge price: " << data.avg_price();    // no endl at the end
+	return os;
+}
+
+#endif

c++ note/chp7/exercise7_3.cpp

@@ -0,0 +1,23 @@
+#include "exercise7_2.h"
+
+int main() {
+	Sales_data total;							// variable to hold the running sum
+	if (read(cin, total)) {						// read the first transaction
+		Sales_data trans;						// variable to hold data for the next transaction
+		while (read(cin, trans)) {				// read the remaining transactions
+			if (total.isbn() == trans.isbn())	// check the isbns
+				total = total.combine(trans);	// update the running total
+			else {
+				print(cout, total) << endl;		// print the results
+				total = trans;					// process the next book
+			}
+		}
+		print(cout, total) << endl;				// print the last transaction
+	}
+	else {										// there was no input
+		cerr << "No data?!" << endl;			// notify the user
+	}
+
+	system("pause");
+	return 0;
+}

c++ note/chp7/exercise7_4.h

@@ -0,0 +1,27 @@
+#ifndef EXERCISE7_4_H_
+#define EXERCISE7_4_H_
+
+#include <string>
+#include <iostream>
+using std::string;
+using std::istream;
+using std::ostream;
+
+struct Person{
+	string name;
+	string address;
+	string getName() const { return name; }
+	string getAddr() const { return address; }
+};
+
+istream& read(istream &is, Person &person){
+	is >> person.name >> person.address;
+	return is;
+}
+
+ostream& print(ostream &os, Person const &person){
+	os << person.name << ' ' << person.address;
+	return os;
+}
+
+#endif