Sunday, August 2, 2009

Should I Learn C First? before C++

The question inevitably arises: "Since C++ is a superset of C, should I learn C first?" Stroustrup and most other C++ programmers agree. Not only is it unnecessary to learn C first, it may be advantageous not to do so. This book attempts to meet the needs of people like you, who come to C++ without prior experience of C. In fact, this book
assumes no programming experience of any kind.



Preparing to Program

C++, perhaps more than other languages, demands that the programmer design the program before writing it. Trivial problems, such as the ones discussed in the first few chapters of this book, don't require much design. Complex problems, however, such as the ones professional programmers are challenged with every day, do require design, and the more thorough the design, the more likely it is that the program will solve the problems it is designed to solve, on
time and on budget. A good design also makes for a program that is relatively bug-free and easy to maintain. It has been estimated that fully 90 percent of the cost of software is the combined cost of debugging and maintenance. Tothe extent that good design can reduce those costs, it can have a significant impact on the bottom-line cost of the project. The first question you need to ask when preparing to design any program is, "What is the problem I'm trying to
solve?" Every program should have a clear, well-articulated goal, and you'll find that even the simplest programs in this book do so. The second question every good programmer asks is, "Can this be accomplished without resorting to writing custom software?" Reusing an old program, using pen and paper, or buying software off the shelf is often a better solution to
a problem than writing something new. The programmer who can offer these alternatives will never suffer from lackof work; finding less-expensive solutions to today's problems will always generate new opportunities later. Assuming you understand the problem, and it requires writing a new program, you are ready to begin your design.

C++ - The ANSI Standard


The Accredited Standards Committee, operating under the procedures of the American National Standards Institute (ANSI), is working to create an international standard for C++. The draft of this standard has been published, and a link is available at www.libertyassociates.com.

The ANSI standard is an attempt to ensure that C++ is portable--that code you write for Microsoft's compiler will compile without errors, using a compiler from any other vendor. Further, because the code in this book is ANSI compliant, it should compile without errors on a Mac, a Windows box, or an Alpha.

For most students of C++, the ANSI standard will be invisible. The standard has been stable for a while, and all the major manufacturers support the ANSI standard. We have endeavored to ensure that all the code in this edition of this book is ANSI compliant.

How C++ Evolved


As object-oriented analysis, design, and programming began to catch on, Bjarne Stroustrup took the most popular language for commercial software development, C, and extended it to provide the features needed to facilitate objectoriented programming. He created C++, and in less than a decade it has gone from being used by only a handful of developers at AT&T to being the programming language of choice for an estimated one million developers. worldwide. It is expected that by the end of the decade, C++ will be the predominant language for commercial software development.

While it is true that C++ is a superset of C, and that virtually any legal C program is a legal C++ program, the leap from C to C++ is very significant. C++ benefited from its relationship to C for many years, as C programmers could ease into their use of C++. To really get the full benefit of C++, however, many programmers found they had to unlearn much of what they knew and learn a whole new way of conceptualizing and solving programming problems.

C++ and Object-Oriented Programming

C++ fully supports object-oriented programming, including the four pillars of object-oriented development: encapsulation, data hiding, inheritance, and polymorphism. Encapsulation and Data Hiding When an engineer needs to add a resistor to the device she is creating, she doesn't typically build a new one from scratch. She walks over to a
bin of resistors, examines the colored bands that indicate the properties, and picks the one she needs. The resistor is a "black box" as far as the engineer is concerned--she doesn't much care how it does its work as long as it conforms to her specifications; she doesn't need to look inside the box to use it in her design.

The property of being a self-contained unit is called encapsulation. With encapsulation, we can accomplish data hiding. Data hiding is the highly valued characteristic that an object can be used without the user knowing or caring how it works internally. Just as you can use a refrigerator without knowing how the compressor works, you can use a well-designed object without knowing about its internal data members.

Similarly, when the engineer uses the resistor, she need not know anything about the internal state of the resistor. All the properties of the resistor are encapsulated in the resistor object; they are not spread out through the circuitry. It is not necessary to understand how the resistor works in order to use it effectively. Its data is hidden inside the resistor's casing.

C++ supports the properties of encapsulation and data hiding through the creation of user-defined types, called classes. You'll see how to create classes on Day 6, "Basic Classes." Once created, a well-defined class acts as a fully encapsulated entity--it is used as a whole unit. The actual inner workings of the class should be hidden. Users of a well-defined class do not need to know how the class works; they just need to know how to use it. Inheritance and Reuse When the engineers at Acme Motors want to build a new car, they have two choices: They can start from scratch, or they can modify an existing model. Perhaps their Star model is nearly perfect, but they'd like to add a turbocharger and a six-speed transmission. The chief engineer would prefer not to start from the ground up, but rather to say, "Let's build another Star, but let's add these additional capabilities. We'll call the new model a Quasar." A Quasar is a kind of Star, but one with new features.

C++ supports the idea of reuse through inheritance. A new type, which is an extension of an existing type, can be declared. This new subclass is said to derive from the existing type and is sometimes called a derived type. The Quasar is derived from the Star and thus inherits all its qualities, but can add to them as needed. Inheritance and its application in C++ are discussed on Day 12, "Inheritance," and Day 15, "Advanced Inheritance." Polymorphism The new Quasar might respond differently than a Star does when you press down on the accelerator. The Quasar might engage fuel injection and a turbocharger, while the Star would simply let gasoline into its carburetor. A user, however, does not have to know about these differences. He can just "floor it," and the right thing will happen, depending on which car he's driving.

C++ supports the idea that different objects do "the right thing" through what is called function polymorphism and class polymorphism. Poly means many, and morph means form. Polymorphism refers to the same name taking many forms, and is discussed on Day 10, "Advanced Functions," and Day 13, "Polymorphism."

Procedural, Structured, and Object-Oriented Programming


Until recently, programs were thought of as a series of procedures that acted upon data. A procedure, or function, is a set of specific instructions executed one after the other. The data was quite separate from the procedures, and the trick in programming was to keep track of which functions called which other functions, and what data was changed. To make sense of this potentially confusing situation, structured programming was created.

The principle idea behind structured programming is as simple as the idea of divide and conquer. A computer program can be thought of as consisting of a set of tasks. Any task that is too complex to be described simply would be broken down into a set of smaller component tasks, until the tasks were sufficiently small and self-contained enough that they were easily understood.

As an example, computing the average salary of every employee of a company is a rather complex task. You can, however, break it down into these subtasks:

1. Find out what each person earns.
2. Count how many people you have.
3. Total all the salaries.
4. Divide the total by the number of people you have.


Totaling the salaries can be broken down into;

1. Get each employee's record.
2. Access the salary.
3. Add the salary to the running total.
4. Get the next employee's record.

In turn, obtaining each employee's record can be broken down into;

1. Open the file of employees.
2. Go to the correct record.
3. Read the data from disk.

Structured programming remains an enormously successful approach for dealing with complex problems. By the late 1980s, however, some of the deficiencies of structured programing had became all too clear.

Second, programmers found themselves constantly reinventing new solutions to old problems. This is often called "reinventing the wheel," and is the opposite of reusability. The idea behind reusability is to build components that have known properties, and then to be able to plug them into your program as you need them. This is modeled after the hardware world--when an engineer needs a new transistor, she doesn't usually invent one, she goes to the big bin of transistors and finds one that works the way she needs it to, or perhaps modifies it. There was no similar option for a software engineer.

Old-fashioned programs forced the user to proceed step-by-step through a series of screens. Modern event-driven programs present all the choices at once and respond to the user's actions.

Object-oriented programming attempts to respond to these needs, providing techniques for managing enormous complexity, achieving reuse of software components, and coupling data with the tasks that manipulate that data.

The essence of object-oriented programming is to treat data and the procedures that act upon the data as a single "object"--a self-contained entity with an identity and certain characteristics of its own.

C++ Getting Started Introduction - Programs


The word program is used in two ways: to describe individual instructions, or source code, created by the programmer, and to describe an entire piece of executable software. This distinction can cause enormous confusion, so we will try to distinguish between the source code on one hand, and the executable on the other.

Source code can be turned into an executable program in two ways: Interpreters translate the source code into computer instructions, and the computer acts on those instructions immediately. Alternatively, compilers translate source code into a program, which you can run at a later time. While interpreters are easier to work with, most serious programming is done with compilers because compiled code runs much faster. C++ is a compiled language.


Solving Problems

The problems programmers are asked to solve have been changing. Twenty years ago, programs were created to manage large amounts of raw data. The people writing the code and the people using the program were all computer professionals. Today, computers are in use by far more people, and most know very little about how computers and programs work. Computers are tools used by people who are more interested in solving their business problems than struggling with the computer.

Ironically, in order to become easier to use for this new audience, programs have become far more sophisticated. Gone are the days when users typed in cryptic commands at esoteric prompts, only to see a stream of raw data. Today's programs use sophisticated "user-friendly interfaces," involving multiple windows, menus, dialog boxes, and the myriad of metaphors with which we've all become familiar. The programs written to support this new approach are far more complex than those written just ten years ago.

As programming requirements have changed, both languages and the techniques used for writing programs have evolved. While the complete history is fascinating, this book will focus on the transformation from procedural programming to object-oriented programming.

A Brief History of C++

Computer languages have undergone dramatic evolution since the first electronic computers were built to assist in telemetry calculations during World War II. Early on, programmers worked with the most primitive computer instructions: machine language. These instructions were represented by long strings of ones and zeroes. Soon, assemblers were invented to map machine instructions to human-readable and -manageable mnemonics, such as ADD and MOV.In time, higher-level languages evolved, such as BASIC and COBOL. These languages let people work with something approximating words and sentences, such as Let I = 100. These instructions were translated back into machine language by interpreters and compilers. An interpreter translates a program as it reads it, turning the program instructions, or code, directly into actions. A compiler translates the code into an intermediary form. This step is called compiling, and produces an object file. The compiler then invokes a linker, which turns the object file into an executable program. Because interpreters read the code as it is written and execute the code on the spot, interpreters are easy for the programmer to work with. Compilers, however, introduce the extra steps of compiling and linking the code, which is inconvenient. Compilers produce a program that is very fast each time it is run. However, the time-consuming task of translating the source code into machine language has already been accomplished. Another advantage of many compiled languages like C++ is that you can distribute the executable program to people who don't have the compiler. With an interpretive language, you must have the language to run the program. For many years, the principle goal of computer programmers was to write short pieces of code that would execute quickly. The program needed to be small, because memory was expensive, and it needed to be fast, because processing power was also expensive. As computers have become smaller, cheaper, and faster, and as the cost of memory has fallen, these priorities have changed. Today the cost of a programmer's time far outweighs the cost of most of the computers in use by businesses. Well-written, easy-to-maintain code is at a premium. Easy- to-maintain means that as business requirements change, the program can be extended and enhanced without great expense.

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Computer Networks The History of Local Area Networks, LAN, The Topologies of a Networks, LANs describe different types of transmission Medias, Local Area Networks Access Methods, Carrier Sense Multiple Access with Collision Detect, Development of LAN Technologies. LAN -Token Ring, LAN Ethernet Digital, LAN - Ethernet Sun microsystems, LAN - Ethernet Mixed Environment, LAN - Token Ring was introduced by IBM LAN - IBM implementation of Token Ring, Token Ring Novell, LAN Token Ring - in a mixed environment, LAN - Fiber Distributed Data Interface, LAN - ATM, LAN Components, LAN Switching Methods, Virtual Local Area Network, Port based VLAN, Mac based VLAN, Protocol based VLAN, User Base VLAN, PC networks Components, PC networks Shared resources, PC Network operating systems, PC networks Novell Netware, PC networks Windows NT, PC networks IBM LAN Server Computer Programming Languages HTML Language, The Generations of Programming Languages, Different types of High Level Languages, Different types of High Level Languages Disadvantages
Computer Networks - IBM LAN Server, Windows NT Networks, Novell Netware, Network operating systems, Networks Shared, Networks Components, User Base, Protocol based, Mac based, Port based, VLAN, LAN Switching, LAN Components, ATM, Fiber Data, Token Ring, Token Ring Novell, IBM implementation, Ethernet, Sun microsystems, Ethernet Digital, Token passing, LAN Technologies, CSMA/CD, Access Methods, Transmission, Networks, The History of Local Area Networks, LAN