Practical C++ Programming, 2nd Edition

Chapter 1. What Is C++?

Profanity is the one language that all programmers understand.

—Anonymous

The ability to organize and process information is the key to success in the modern age. Computers are designed to handle and process large amounts of information quickly and efficiently. However, they can’t do anything until someone tells them what to do. That’s where C++ comes in. C++ is a high-level programming language that allows a software engineer to efficiently communicate with a computer.

C++ is a highly flexible and adaptable language. Since its creation in 1980, it has been used for a wide variety of programs including firmware for microcontrollers, operating systems, applications, and graphics programming. C++ is the programming language of choice for a tremendous number of applications. There is a tremendous demand for people who can tell computers what to do, and C++ lets you do so quickly and efficiently.

A Brief History of C++

In 1970 two programmers, Brian Kernighan and Dennis Ritchie, created a new language called C. (The name came about because C was preceded by the old programming language they were using called B.) C was designed with one goal in mind: writing operating systems. The language was extremely simple and flexible and soon was used for many different types of programs. It quickly became one of the most popular programming languages in the world.

C had one major problem, however. It was a procedure-oriented language. This meant that in designing a typical C program, the programmer would start by describing the data and then write procedures to manipulate that data.

Programmers eventually discovered that it made a program clearer and easier to understand if they were able to take a bunch of data and group it together with the operations that worked on that data. Such a grouping is called an object or class. Designing programs by designing classes is known as object-oriented design (OOD).

In 1980 Bjarne Stroustrup started working on a new language, called “C with Classes.” This language improved on C by adding a number of new features, the most important of which was classes. This language was improved, augmented, and finally became C++.

C++ owes its success to the fact that it allows the programmer to organize and process information more effectively than most other languages. Also, it builds on the work already done with the C language. In fact, most C programs can be transformed into C++ programs with little trouble. These programs usually don’t use all the new features of C++, but they do work. In this way, C++ allows programmers to build on an existing base of C code.

C++ Organization

C++ is designed as a bridge between the programmer and the raw computer. The idea is to let the programmer organize a program in a way that he can easily understand. The compiler then translates the language into something the machine can use.

Computer programs consist of two main parts: data and instructions. The computer imposes little or no organization on these two parts. After all, computers are designed to be as general as possible. The idea is for the programmer to impose his or her own organization on the computer and not the other way around.

The data in a computer is stored as a series of bytes. C++ organizes those bytes into useful data. Data declarations are used by the programmer to describe the information he or she is working with. For example:

int total;	    // Total number accounts

tells C++ that you want to use a section of the computer’s memory to store an integer named total. You can let the compiler decide what particular bytes of memory to use; that’s a minor bookkeeping detail you don’t need to worry about.

The variable total is a simple variable . It can hold only one integer and describe only one total. A series of integers can be organized into an array. Again, C++ will handle the details, imposing that organization on the computer’s memory.

int balance[100];   // Balance (in cents) for all 100 accounts

Finally, there are more complex data types. For example, a rectangle might have a width, a height, a color, and a fill pattern. C++ lets you organize these four attributes into one group called a structure .

struct rectangle {
    int width;      	  	// Width of rectangle in pixels
    int height;     	  	// Height of rectangle in pixels 	 
    color_type color;	        // Color of the rectangle 	 
    fill_type fill;	        // Fill pattern 	
};

However, data is only one part of a program; you also need instructions. As far as the computer is concerned, it knows nothing about the layout of the instructions. It knows only what it’s doing for the current instruction and where to get the next instruction.

C++ is a high-level language. It lets you write a high-level statement such as:

area = (base * height) / 2.0;	    // Compute area of triangle

The compiler translates this statement into a series of cryptic machine instructions. This sort of statement is called an assignment statement . It is used to compute and store the value of an arithmetic expression.

You can also use control statements to control the order of processing. Statements such as the if and switch statements enable the computer to make simple decisions. Statements can be repeated by using looping statements such as while and for.

Groups of statements can be wrapped to form functions. Thus you only need to write a general-purpose function to draw a rectangle once, and you can reuse that function whenever you want to draw a new rectangle. C++ provides a rich set of standard functions that perform common functions such as searching, sorting, input, and output. A set of related functions can be grouped together to form a module , and modules are linked to form programs .

One of the major goals of the C++ language is to organize instructions into reusable components. After all, you can write programs much faster if you “borrow” most of your code from somewhere else. Groups of reusable modules can be combined into a library. For example, if you need a sort routine, you can use the standard function qsort from the library and link it into your program.

A computer divides the world into data and instructions. For a long time, high-level languages such as C kept that dividing line in place. In C you can define data or write instructions, but you can’t combine the two.

One of C++’s major innovations is the idea of combining data and instructions together in a construct called a class or object. Object-oriented programming allows you to group data with the operations that can be performed on that data. This concept is taken a step further in C++ by letting you derive new classes from existing ones.

This last feature is extremely powerful. It allows you to build complex classes on top of smaller, simpler ones. It also allows you to define a basic, abstract class and then derive specific classes from it. For example, an abstract class of shape might be used to define the shapes rectangle, triangle, and circle.

Organization is the key to writing good programs. In this book, you know that the table of contents is in the front and the index is in the back, because that’s the way books are organized. Organization makes this book easier to use.

The C++ language lets you organize your programs using a simple yet powerful syntax. This book goes beyond the C++ syntax and teaches you style rules that enable you to create highly readable and reliable programs. By combining a powerful syntax with good programming style, you can create powerful programs that perform complex and wonderful operations.

How to Learn C++

The only way to learn how to program is to write programs. You’ll learn a lot more by writing and debugging programs than you ever will by reading this book. This book contains many programming exercises, and you should try to do as many of them as possible. When doing the exercises, keep good programming style in mind. Always comment your programs, even if you’re doing the exercises only for yourself. Commenting helps you organize your thoughts, and commenting your own programs is good practice for when you go into the “real world.”

Don’t let yourself be seduced by the idea that, “I’m only writing these programs for myself, so I don’t need to comment them.” First of all, code that looks obvious to you when you write it can often be confusing and cryptic when you revisit it a week later. Writing comments also helps you organize your ideas. (If you can write out an idea in English, you are halfway to writing it in C++.)

Finally, programs tend to be around far longer than expected. I once wrote a highly system-dependent program that was designed to work only on the computer at CalTech. As I was the only one who would ever use the program, it would print the following message if I got the command line wrong:

?LSTUIT User is a twit

A few years later I was a student at Syracuse University. The chief secretary at the School of Computer Science needed a program similar to my CalTech listing program, so I adapted my program for her use. Unfortunately, I had forgotten about my funny little error message.

Imagine how horrified I was when I came into the Computer Science office and was accosted by the chief secretary. This lady had so much power she could make the dean cringe. She looked at me and said, “User is a twit, huh?” Luckily she had a sense of humor, or I might not be here today.

Sprinkled throughout are not only examples of working programs (to show you how to do things), but also examples of broken programs where we ask you to go through the program and figure out what’s wrong. Often the problem is very subtle, such as a misplaced semicolon or use of = instead of ==. These programs let you learn how to spot mistakes in a small program. That way when you make similar mistakes in a big program—and you will make mistakes—you will be trained to spot them.