• The user usually provides such a value by typing it using the keyboard

The cin operator is used for that purpose

• (Pronounce “see in”)
• It displays a blinking cursor on the monitor to let the user know that a value is expected
• Uses two greater than signs “>>” followed by the name of the expected value (A-1)

Example of (A-1)

cin >> valueName;

If you are requesting many values from the user

• You can write a statement that would act accordingly by separating values with as many >> operators as necessary (A-2)

Example of (A-2)

cin >> firstName >> lastName >> age;

• (B-1) Two types of storage spaces

(B-1) The hard drive

• A static storage area that keeps its information all the time, almost regardless of what happens to your computer

(B-1) Random Access Memory (RAM)

• This storage area keeps its information only when the computer is turned on. This means that the RAM loses its Information when the computer is turned off

When the user “opens” or launches a program

• Part of the program “goes” into the RAM

If or when the application is not used anymore, which means that if the user “closes” the application

• The part of memory that the application was using in the RAM is gone and the memory space that the application was using becomes available

When your program opens

• Part of your application gets “loaded” into the RAM

When the user is using your application

• The information that your application requests also goes into the RAM while your application is processing such requests

Before using such a variable

• You must first let the compiler know

Letting the compiler know about a variable is referred to

• “Declaring” the variable

The compiler will need two pieces of information concerning each variable

• The amount of space the variable will need
• A name to recognize that variable

• The myfirst.cpp program (A-1)
• Uses the following C++ statement (A-2):
• The part enclosed within the double quotation marks is the message to print
  • In C++, any series of characters enclosed in double quotation marks is called a character string, presumably because it consists of several characters strung together into a larger unit
• The << notation indicates that the statement is sending the string to cout; the symbols point the way the information flows
• And what is cout?
  •  It’s a predefined object that knows how to display a variety of things, including strings, numbers, and individual characters
    • (An object is a particular instance of a class, and a class defines how data is stored and used.)

Example of (A-1)

// myfirst.cpp--displays a message
#include <iostream>				// a PREPROCESSOR directive
int main()					// function header
{						// start of function body
	using namespace std;			// make definitions visible
	cout << "Come up and C++ me some time.";	// message
	cout << endl;				// start a new line
	cout << "You won't regret it!" << endl;	// more output
	return 0;					// terminate main()
}

                


Example of (A-2)

cout << "Come up and C++ me some time.";

Well, using objects so soon is a bit awkward because you won’t learn about objects for several more chapters

• Actually, this reveals one of the strengths of objects
  • You don’t have to know the innards of an object in order to use it
    • All you must know is its interface—that is, how to use it

The cout object has a simple interface

• If string represents a string, you can do the following to display it (A-3):

Example of (A-3)

cout << string;

This is all you must know to display a string, but now take a look at how the C++ conceptual view represents the process

• In this view, the output is a stream—that is, a series of characters flowing from the program
  • The cout object, whose properties are defined in the iostream file, represents that stream
    • The object properties for cout include an insertion operator (<<) that inserts the information on its right into the stream

Consider the following statement (note the terminating semicolon) (A-4)

• It inserts the string “Come up and C++ me some time.” into the output stream
  • Thus, rather than say that your program displays a message, you can say that it inserts a string into the output stream
    • Somehow, that sounds more impressive
      •  See (Image-1)

Example of (A-4)

cout << "Come up and C++ me some time.";

(Image-1) Displaying a string by using cout

A First Look at Operator Overloading

If you’re coming to C++ from C

• You probably noticed that the insertion operator (<<) looks just like the bitwise left-shift operator (<<)
  • This is an example of operator overloading, by which the same operator symbol can have different meanings
    • The compiler uses the context to figure out which meaning is intended

C itself has some operator overloading

• For example, the & symbol represents both the address operator and the bitwise AND operator
  • The * symbol represents both multiplication and dereferencing a pointer
    • The important point here is not the exact function of these operators but that the same symbol can have more than one meaning, with the compiler determining the proper meaning from the context
      • (You do much the same when you determine the meaning of “sound” in “sound card” versus “sound financial basis.”)

C++ extends the operator overloading concept

• By letting you redefine operator meanings for the user-defined types called classes

• Instructions can be treated as assignments

Assignment will be…

• Called a function

The primary function used in C++

• Is called main

Function’s name is

• Followed by an opening and a closing parentheses

Main function will always be written

• At least as main()

When a program is written and you ask the computer to “execute” it, the first thing to look for

• Is the main() function
• This means that every C++ program should have the main() function

Function has

• A body; this is where the behavior (assignment) of the function would be “described”

 


The body of a function

• Starts with an opening curly bracket “{” and closes with a closing curly bracket “}“
• Everything in the curly brackets belongs to, or is part of, the function

The main() function can be written as (A-1):


Example of (A-1)

main(){}

Whenever you create a program

• It is important to isolate any inclusion of a library on its own line (A-2)

Example of (A-2)

#include <iostream>
using namespace std;
main(){}

• A  section of code
• Delimited and referred to using a specific name
• Give a common name to that portion of code so that, when referring to it, only entities that are part of that section would referred to

A namespace is created to

• Set apart a portion of code with the goal to reduce, otherwise eliminate, confusion

How to use namespace

• Type the using namespace expression followed by the name of the namespace and a semi-colon (A-1)

Example of (A-1)

using namespace thebasic;

One of the namespaces used in C++

• Is called std (A-2)
  • After typing this, any part of the namespace becomes available to you

Example of (A-2)

using namespace std;

The iostream library

• Is part of the std namespace
  • When you use it, you don’t need to include the extended of the iostream file

You can start your program with (A-3):


Example of (A-3)

#include <iostream>
using namespace std;

• (Also) called header files
• And, as computer files
• They have the extension “.h”
• house.h
• person.h
• They could have any name

iostream

• Asks the computer to display stuff on the monitor’s screen

How to put a library in your program

• Put it at the beginning of the file (A-1)

Example of (A-1)

iostream.h

How to use a library in your program

• Simply include it by using the word “include” before the name of the library (A-2)

Example of (A-2)

include iostream.h

The pound sign “#”

• Append the sign when you want the computer to “know” that the word “include” means , “I want to include the following library” (A-3)

 
Example of (A-3)

#include iostream.h

There are usually two kinds of libraries or files you will use in your programs

• Libraries that came with C++
• Those that you write

To include your own library

• Enclose it between double quotes (A-4)

Example of (A-4)

#include "books.h"

To include the library that came with C++

• Enclose it between < and > (A-5)

Example of (A-5)

#include <iostream.h>

You can add as many libraries

• As you see fit