Cpp Primer Chapter 1

Starting from today, I will read and write notes for C++ primer. I will only write notes that I think that is important, so not all the contents will be covered.

Design a bookstore

Our store keeps a file of transactions, each of which records the sale of one or more copies of a single book. Each transaction contains three data elements:

     0-201-70353-X 4 24.99

The first element is an ISBN (International Standard Book Number, a unique book identifier), the second is the number of copies sold, and the last is the price at which each of these copies was sold.

main

Original

#include <iostream>
#include "Sales_item.h"
int main() {
  Sales_item book;
  // read ISBN, number of copies sold, and sales price
  std::cin >> book;
  // write ISBN, number of copies sold, total revenue, and average price 
  std::cout << book << std::endl;
  return 0; 
}

Adding Sales_items

#include <iostream>
#include "Sales_item.h"
int main() {
  Sales_item item1, item2;
  std::cin >> item1 >> item2; // read a pair of transactions 
  std::cout << item1 + item2 << std::endl; // print their sum
  return 0; 
}

Completed main

#include <iostream>
#include "Sales_item.h"
int main() {
  Sales_item total; // variable to hold data for the next transaction
	// read the first transaction and ensure that there are data to process 
  if (std::cin >> total) {
		Sales_item trans; // variable to hold the running sum 
		// read and process the remaining transactions
		while (std::cin >> trans) { // if we’re still processing the same book
			if (total.isbn() == trans.isbn())
				total += trans; // update the running total 
      else { // print results for the previous book
        std::cout << total << std::endl;
        total = trans; // total now refers to the next book
      } 
    }
    std::cout << total << std::endl; // print the last transaction 
  } else { // no input! warn the user
    std::cerr << "No data?!" << std::endl; 
    return -1; // indicate failure
  }
  return 0; 
}

Only if the isbn of two books are the same can we add them together.

Get the status code returned by main()

The value returned from main is accessed in a system-dependent manner. On both UNIX and Windows systems, after executing the program, you must issue an appropriate echo command.

On UNIX systems, we obtain the status by writing

\$ echo $?

To see the status on a Windows system, we write

$ echo %ERRORLEVEL%

Exercise 1.16

Write your own version of a program that prints the sum of a set of integers read from cin.

#include <iostream>
int main()
{
    int sum = 0;
  	// read in until no input or empty input
    for (int val; std::cin >> val; sum += val);
    std::cout << sum << std::endl;

    return 0;
}

Class

To use a class we need to know three things:

• What is its name?
• Where is it defined?
• What operations does it support?

Terms

1. From std::cout << "Enter two numbers:"; std::cout << std::endl;, the message is a string literal, The second operator prints endl, which is a special value called a manipulator.
2. The prefix std:: indicates that the names cout and endl are defined inside the namespace named std. Namespace allows us to avoid inadvertent collision between the names we defined and uses of those same names inside a library.
3. Conventionally, header file names are derived from the name of a class defined in that header. Header files that we write usually have a suffix of .h, but some programmers use .H, .hpp, or .hxx.