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

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

Exercise 7.3: Revise your transaction-processing program from § 7.1.1 (p.256) to use these members.

exercsie7_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.

#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.

#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.

Exercise 7.11: Add constructors to your Sales_data class and write a program to use each of the constructors.

exercise7_11.h

exercise7_11.cpp

Exercise 7.12: Move the definition of the Sales_data constructor that takes an istream into the body of the Sales_data class.

struct Sales_data {
	string bookNo;
	unsigned units_sold = 0;
	double revenue = 0.0;

	//constructors
	Sales_data() = default;
	Sales_data(istream &is){
		double price;
		is << bookNo << units_sold << price;
		revenue = price * units_sold;
	}
	Sales_data(string isbn) : bookNo(isbn) {};
	Sales_data(string isbn, unsigned n, double price) : bookNo(isbn), units_sold(n), revenue(n * price) {};

	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
};

Exercise 7.13: Rewrite the program from page 255 to use the istream constructor.

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

	system("pause");
	return 0;
}

This can be weird, for the cin operation is seperated from the if-condition.

Exercise 7.14: Write a version of the default constructor that explicitly initializes the members to the values we have provided as in-class initializers.

struct Sales_data {
	string bookNo;
	unsigned units_sold;
	double revenue;

	//constructors
	Sales_data(){units_sold = 0, revenue = 0.0;}
	Sales_data(istream &is){
		double price;
		is << bookNo << units_sold << price;
		revenue = price * units_sold;
	}
	Sales_data(string isbn) : bookNo(isbn) {};
	Sales_data(string isbn, unsigned n, double price) : bookNo(isbn), units_sold(n), revenue(n * price) {};

	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
};

But there's a drawback in this manner. For example, in constructor3, Sales_data(string isbn), we also have to explicitly initializes all the members, which causes redundance.

Exercise 7.15: Add appropriate constructors to your Person class.

exercise7_15.h

exercise7_15.cpp

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Solutions to Exercises in Chapter Seven

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