C++ Beginner's Guide CH01

C++ A Beginner’s Guide by Herbert Schildt Module 1 C++ Fundamentals Table of Contents CRITICAL SKILL 1.1: A Brief History of C++ .................................................................................................... 2 CRITICAL SKILL 1.2: How C++ Relates to Java and C#.................................................................................... 5 CRITICAL SKILL 1.3: Object-Oriented Programming ...................................................................................... 7 CRITICAL SKILL 1.4: A First Simple Program ................................................................................................ 10 CRITICAL SKILL 1.5: A Second Simple Program ........................................................................................... 15 CRITICAL SKILL 1.6: Using an Operator ....................................................................................................... 17 CRITICAL SKILL 1.7: Reading Input from the Keyboard ............................................................................... 19 Project 1-1 Converting Feet to Meters ....................................................................................................... 24 CRITICAL SKILL 1.8: Two Control Statements.............................................................................................. 26 CRITICAL SKILL 1.9: Using Blocks of Code ................................................................................................... 30 Project 1-2 Generating a Table of Feet to Meter Conversions ................................................................... 33 CRITICAL SKILL 1.10: Introducing Functions................................................................................................ 35 CRITICAL SKILL 1.11: The C++ Keywords ..................................................................................................... 38 CRITICAL SKILL 1.12: Identifiers................................................................................................................... 39 If there is one language that defines the essence of programming today, it is C++. It is the preeminent language for the development of high-performance software. Its syntax has become the standard for professional programming languages, and its design philosophy reverberates throughout computing. C++ is also the language from which both Java and C# are derived. Simply stated, to be a professional programmer implies competency in C++. It is the gateway to all of modern programming. The purpose of this module is to introduce C++, including its history, its design philosophy, and several of its most important features. By far, the hardest thing about learning a programming language is the fact that no element exists in isolation. Instead, the components of the language work together. This interrelatedness makes it difficult to discuss one aspect of C++ without involving others. To help overcome this problem, this module provides a brief overview of several C++ features, including the general form of a C++ program, some basic control statements, and operators. It does not go into too many details, but rather concentrates on the general concepts common to any C++ program. CRITICAL SKILL 1.1: A Brief History of C++ The history of C++ begins with C. The reason for this is easy to understand: C++ is built upon the foundation of C. Thus, C++ is a superset of C. C++ expanded and enhanced the C language to support object-oriented programming (which is described later in this module). C++ also added several other improvements to the C language, including an extended set of library routines. However, much of the spirit and flavor of C++ is directly inherited from C. Therefore, to fully understand and appreciate C++, you need to understand the “how and why” behind C. C: The Beginning of the Modern Age of Programming The invention of C defines the beginning of the modern age of programming. Its impact should not be underestimated because it fundamentally changed the way programming was approached and thought about. Its design philosophy and syntax have influenced every major language since. C was one of the major, revolutionary forces in computing. C was invented and first implemented by Dennis Ritchie on a DEC PDP-11 using the UNIX operating system. C is the result of a development process that started with an older language called BCPL. BCPL was developed by Martin Richards. BCPL influenced a language called B, which was invented by Ken Thompson and which led to the development of C in the 1970s. Prior to the invention of C, computer languages were generally designed either as academic exercises or by bureaucratic committees. C was different. It was designed, implemented, and developed by real, working programmers, reflecting the way they approached the job of programming. Its features were honed, tested, thought about, and rethought by the people who actually used the language. As a result, C attracted many proponents and quickly became the language of choice of programmers around the world. C grew out of the structured programming revolution of the 1960s. Prior to structured programming, large programs were difficult to write because the program logic tended to degenerate into what is known as “spaghetti code,” a tangled mass of jumps, calls, and returns that is difficult to follow. Structured languages addressed this problem by adding well-defined control statements, subroutines with local variables, and other improvements. Using structured languages, it became possible to write moderately large programs. Although there were other structured languages at the time, such as Pascal, C was the first to successfully combine power, elegance, and expressiveness. Its terse, yet easy-to-use syntax coupled with its philosophy that the programmer (not the language) was in charge quickly won many converts. It can be a bit hard to understand from today’s perspective, but C was a breath of fresh air that programmers had long awaited. As a result, C became the most widely used structured programming language of the 1980s. The Need for C++ Given the preceding discussion, you might be wondering why C++ was invented. Since C was a successful computer programming language, why was there a need for something else? The answer is complexity. Throughout the history of programming, the increasing complexity of programs has driven the need for better ways to manage that complexity. C++ is a response to that need. To better understand the correlation between increasing program complexity and computer language development, consider the following. Approaches to programming have changed dramatically since the invention of the computer. For example, when computers were first invented, programming was done by using the computer’s front panel to toggle in the binary machine instructions. As long as programs were just a few hundred instructions long, this approach worked. As programs grew, assembly language was invented so that programmers could deal with larger, increasingly complex programs by using symbolic representations of the machine instructions. As programs continued to grow, high-level languages were developed to give programmers more tools with which to handle the complexity. The first widely used computer language was, of course, FORTRAN. While FORTRAN was a very impressive first step, it is hardly a language that encourages clear, easy-to-understand programs. The 1960s gave birth to structured programming, which is the method of programming encouraged by languages such as C. With structured languages it was, for the first time, possible to write moderately complex programs fairly easily. However, even with structured programming methods, once a project reaches a certain size, its complexity exceeds what a programmer can manage. By the late 1970s, many projects were near or at this point. In response to this problem, a new way to program began to emerge: object-oriented programming (OOP). Using OOP, a programmer could handle larger, more complex programs. The trouble was that C did not support object-oriented programming. The desire for an object-oriented version of C ultimately led to the creation of C++. In the final analysis, although C is one of the most liked and widely used professional programming languages in the world, there comes a time when its ability to handle complexity is exceeded. Once a program reaches a certain size, it becomes so complex that it is difficult to grasp as a totality. The purpose of C++ is to allow this barrier to be broken and to help the programmer comprehend and manage larger, more complex programs. C++ Is Born C++ was invented by Bjarne Stroustrup in 1979, at Bell Laboratories in Murray Hill, New Jersey. He initially called the new language “C with Classes.” However, in 1983 the name was changed to C++. Stroustrup built C++ on the foundation of C, including all of C’s features, attributes, and benefits. He also adhered to C’s underlying philosophy that the programmer, not the language, is in charge. At this point, it is critical to understand that Stroustrup did not create an entirely new programming language. Instead, he enhanced an already highly successful language. Most of the features that Stroustrup added to C were designed to support object-oriented programming. In essence, C++ is the object-oriented version of C. By building upon the foundation of C, Stroustrup provided a smooth migration path to OOP. Instead of having to learn an entirely new language, a C programmer needed to learn only a few new features before reaping the benefits of the object-oriented methodology. When creating C++, Stroustrup knew that it was important to maintain the original spirit of C, including its efficiency, flexibility, and philosophy, while at the same time adding support for object-oriented programming. Happily, his goal was accomplished. C++ still provides the programmer with the freedom and control of C, coupled with the power of objects. Although C++ was initially designed to aid in the management of very large programs, it is in no way limited to this use. In fact, the object-oriented attributes of C++ can be effectively applied to virtually any programming task. It is not uncommon to see C++ used for projects such as editors, databases, personal file systems, networking utilities, and communication programs. Because C++ shares C’s efficiency, much high-performance systems software is constructed using C++. Also, C++ is frequently the language of choice for Windows programming. The Evolution of C++ Since C++ was first invented, it has undergone three major revisions, with each revision adding to and altering the language. The first revision was in 1985 and the second in 1990. The third occurred during the C++ standardization process. Several years ago, work began on a standard for C++. Toward that end, a joint ANSI (American National Standards Institute) and ISO (International Standards Organization) standardization committee was formed. The first draft of the proposed standard was created on January 25, 1994. In that draft, the ANSI/ISO C++ committee (of which I was a member) kept the features first defined by Stroustrup and added some new ones. But, in general, this initial draft reflected the state of C++ at the time. Soon after the completion of the first draft of the C++ standard, an event occurred that caused the standard to be greatly expanded: the creation of the Standard Template Library (STL) by Alexander Stepanov. The STL is a set of generic routines that you can use to manipulate data. It is both powerful and elegant. But it is also quite large. Subsequent to the first draft, the committee voted to include the STL in the specification for C++. The addition of the STL expanded the scope of C++ well beyond its original definition. While important, the inclusion of the STL, among other things, slowed the standardization of C++. It is fair to say that the standardization of C++ took far longer than anyone had expected. In the process, many new features were added to the language, and many small changes were made. In fact, the version of C++ defined by the ANSI/ISO C++ committee is much larger and more complex than Stroustrup’s original design. The final draft was passed out of committee on November 14, 1997, and an ANSI/ISO standard for C++ became a reality in 1998. This is the specification for C++ that is usually referred to as Standard C++. The material in this book describes Standard C++. This is the version of C++ supported by all mainstream C++ compilers, including Microsoft’s Visual C++. Thus, the code and information in this book are fully portable. CRITICAL SKILL 1.2: How C++ Relates to Java and C# In addition to C++, there are two other important, modern programming languages: Java and C#. Java was developed by Sun Microsystems, and C# was created by Microsoft. Because there is sometimes confusion about how these two languages relate to C++, a brief discussion of their relationship is in order. C++ is the parent for both Java and C#. Although both Java and C# added, removed, and modified various features, in total the syntax for these three languages is nearly identical. Furthermore, the object model used by C++ is similar to the ones used by Java and C#. Finally, the overall “look and feel” of these languages is very similar. This means that once you know C++, you can easily learn Java or C#. The opposite is also true. If you know Java or C#, learning C++ is easy. This is one reason that Java and C# share C++’s syntax and object model; it facilitated their rapid adoption by legions of experienced C++ programmers. The main difference between C++, Java, and C# is the type of computing environment for which each is designed. C++ was created to produce high-performance programs for a specific type of CPU and operating system. For example, if you want to write a program that runs on an Intel Pentium under the Windows operating system, then C++ is the best language to use. Ask the Expert Q: How do Java and C# create cross-platform, portable programs, and why can’t C++ do the same? A: Java and C# can create cross-platform, portable programs and C++ can’t because of the type of object code produced by the compiler. In the case of C++, the output from the compiler is machine code that is directly executed by the CPU. Thus, it is tied to a specific CPU and operating system. If you want to run a C++ program on a different system, you need to recompile it into machine code specifically targeted for that environment. To create a C++ program that would run in a variety of environments, several different executable versions of the program are needed. Java and C# achieve portability by compiling a program into a pseudocode, intermediate language. In the case of Java, this intermediate language is called bytecode. For C#, it is called Microsoft Intermediate Language (MSIL). In both cases, this pseudocode is executed by a runtime system. For Java, this runtime system is called the Java Virtual Machine (JVM). For C#, it is the Common Language Runtime (CLR). Therefore, a Java program can run in any environment for which a JVM is available, and a C# program can run in any environment in which the CLR is implemented. Since the Java and C# runtime systems stand between a program and the CPU, Java and C# programs incur an overhead that is not present in the execution of a C++ program. This is why C++ programs usually run faster than the equivalent programs written in Java or C#. Java and C# were developed in response to the unique programming needs of the online environment of the Internet. (C# was also designed to simplify the creation of software components.) The Internet is connected to many different types of CPUs and operating systems. Thus, the ability to produce cross- platform, portable programs became an overriding concern. The first language to address this need was Java. Using Java, it is possible to write a program that runs in a wide variety of environments. Thus, a Java program can move about freely on the Internet. However, the price you pay for portability is efficiency, and Java programs execute more slowly than do C++ programs. The same is true for C#. In the final analysis, if you want to create high-performance software, use C++. If you need to create highly portable software, use Java or C#. One final point: Remember that C++, Java, and C# are designed to solve different sets of problems. It is not an issue of which language is best in and of itself. Rather, it is a question of which language is right for the job at hand. 1. From what language is C++ derived? 2. What was the main factor that drove the creation of C++? 3. C++ is the parent of Java and C#. True or False? Answer Key: 1. C++ is derived from C. 2. Increasing program complexity was the main factor that drove the creation of C++. 3. True. CRITICAL SKILL 1.3: Object-Oriented Programming Central to C++ is object-oriented programming (OOP). As just explained, OOP was the impetus for the creation of C++. Because of this, it is useful to understand OOP’s basic principles before you write even a simple C++ program. Object-oriented programming took the best ideas of structured programming and combined them with several new concepts. The result was a different and better way of organizing a program. In the most general sense, a program can be organized in one of two ways: around its code (what is happening) or around its data (who is being affected). Using only structured programming techniques, programs are typically organized around code. This approach can be thought of as “code acting on data.” Object-oriented programs work the other way around. They are organized around data, with the key principle being “data controlling access to code.” In an object-oriented language, you define the data and the routines that are permitted to act on that data. Thus, a data type defines precisely what sort of operations can be applied to that data. To support the principles of object-oriented programming, all OOP languages, including C++, have three traits in common: encapsulation, polymorphism, and inheritance. Let’s examine each. Encapsulation Encapsulation is a programming mechanism that binds together code and the data it manipulates, and that keeps both safe from outside interference and misuse. In an object-oriented language, code and data can be bound together in such a way that a self-contained black box is created. Within the box are all necessary data and code. When code and data are linked together in this fashion, an object is created. In other words, an object is the device that supports encapsulation. Ask the Expert Q: I have heard the term method applied to a subroutine. Is a method the same as a function? A: In general, the answer is yes. The term method was popularized by Java. What a C++ programmer calls a function, a Java programmer calls a method. C# programmers also use the term method. Because it is becoming so widely used, sometimes the term method is also used when referring to a C++ 7 C++ A Beginner’s Guide by Herbert Schildt C++ A Beginner’s Guide by Herbert Schildt function. Within an object, code or data or both may be private to that object or public. Private code or data is known to and accessible by only another part of the object. That is, private code or data cannot be accessed by a piece of the program that exists outside the object. When code or data is public, other parts of your program can access it even though it is defined within an object. Typically, the public parts of an object are used to provide a controlled interface to the private elements of the object. C++’s basic unit of encapsulation is the class. A class defines the form of an object. It specifies both the data and the