C++ Lecture 01

Introduction

Terms such as ‘‘the Internet,’’ which were unfamiliar just 20 years ago are now common. Students in elementary school regularly ‘‘surf ’’ the Internet and use computers to design their classroom projects. Many people use the Internet to look for information and to communicate with others. This is all made possible by the availability of different software, also known as computer programs. Without software, a computer is useless. Software is developed by using programming languages. The programming language C++ is especially well suited for developing software to accomplish specific tasks. Our main objective is to help you learn how to write programs in the C++ programming language. Before you begin programming, it is useful to understand some of the basic terminology and different components of a computer. We begin with an overview of the history of computers.

A Brief Overview of the History of Computers

The first device known to carry out calculations was the abacus. The abacus was invented in Asia but was used in ancient Babylon, China, and throughout Europe until the late middle ages. The abacus uses a system of sliding beads in a rack for addition and subtraction. In 1642, the French philosopher and mathematician Blaise Pascal invented the calculating device called the Pascaline. It had eight movable dials on wheels and could calculate sums up to eight figures long. Both the abacus and Pascaline could perform only addition and subtraction operations. Later in the 17th century, Gottfried von Leibniz invented a device that was able to add, subtract, multiply, and divide. In 1819, Joseph Jacquard, a French weaver, discovered that the weaving instructions for his looms could be stored on cards with holes punched in them. While the cards moved through the loom in sequence, needles passed through the holes and picked up threads of the correct color and texture. A weaver could rearrange the cards and change the pattern being woven. In essence, the cards programmed a loom to produce patterns in cloth. The weaving industry may seem to have little in common with the computer industry. However, the idea of storing information by punching holes on a card proved to be of great importance in the later development of computers.

In the early and mid-1800s, Charles Babbage, an English mathematician and physical scientist, designed two calculating machines—the difference engine and the analytical engine. The difference engine could perform complex operations such as squaring numbers automatically. Babbage built a prototype of the difference engine, but the actual device was never produced. The analytical engine’s design included input device, data storage, a control unit that allowed processing instructions in any sequence, and output devices. However, the designs remained in blueprint stage. Most of Babbage’s work is known through the writings of his colleague Ada Augusta, Countess of Lovelace. Augusta is considered the first computer programmer.

At the end of the 19th century, U.S. Census officials needed help in accurately tabulating the census data. Herman Hollerith invented a calculating machine that ran on electricity and used punched cards to store data. Hollerith’s machine was immensely successful. Hollerith founded the Tabulating Machine Company, which later became the computer and technology corporation known as  IBM.

The first computer-like machine was the Mark I. It was built, in 1944, jointly by IBM and Harvard University under the leadership of Howard Aiken. Punched cards were used to feed data into the machine. The Mark I was 52 feet long, weighed 50 tons, and had 750,000 parts. In 1946, the ENIAC (Electronic Numerical Integrator and Calculator) was built at the University of Pennsylvania. It contained 18,000 vacuum tubes and weighed some 30 tons.

The computers that we know today use the design rules given by John von Neumann in the late 1940s. His design included components such as an arithmetic logic unit, a control unit, memory, and input/output devices. These components are described in the next section. Von Neumann’s computer design makes it possible to store the programming instructions and the data in the same memory space. In 1951, the UNIVAC (Universal Automatic Computer) was built and sold to the U.S. Census  Bureau.

In 1956, the invention of transistors resulted in smaller, faster, more reliable, and more energy-efficient computers. This era also saw the emergence of the software development industry, with the introduction of FORTRAN and COBOL, two early programming languages. In the next major technological advancement, transistors were replaced by tiny integrated circuits, or ‘‘chips.’’ Chips are smaller and cheaper than transistors and can contain thousands of circuits on a single chip. They give computers tremendous processing speed.

In 1970, the microprocessor, an entire CPU on a single chip, was invented. In 1977, Stephen Wozniak and Steven Jobs designed and built the first Apple computer in their garage. In 1981, IBM introduced its personal computer (PC). In the 1980s, clones of the IBM PC made the personal computer even more affordable. By the mid-1990s, people from many walks of life were able to afford them. Computers continue to become faster and less expensive as technology advances.

Modern-day computers are powerful, reliable, and easy to use. They can accept spoken-word instructions and imitate human reasoning through artificial intelligence. Expert systems assist doctors in making diagnoses. Mobile computing applications are growing significantly. Using handheld devices, delivery drivers can access global positioning satellites (GPS) to verify customer locations for pickups and deliveries. Cell phones permit you to check your e-mail, make airline reservations, see how stocks are performing, and access your bank accounts.

Although there are several categories of computers, such as mainframe, midsize, and micro, all computers share some basic elements, described in the next section.

Elements of a Computer System

A computer is an electronic device capable of performing commands. The basic commands that a computer performs are input (get data), output (display result), storage, and perfor- mance of arithmetic and logical operations.

In  today’s  market,  personal  computers  are  sold  with  descriptions  such  as  a  Pentium  4 Processor 2.80 GHz, 1 GB RAM, 250 GB HD, VX750 19" Silver Flat  CRT  Color  Monitor, preloaded with software such as an operating system, games, encyclopedias, and application software such as word processors or money management programs. These descriptions represent  two categories:  hardware and software. Items  such  as ‘‘Pentium  4

Processor 2.80 GHz, 1GB RAM, 250 GB HD, VX750 19" Silver Flat CRT Color Monitor’’ fall into the hardware category; items such as ‘‘operating system, games, encyclopedias, and application software’’ fall into the software category. Let’s consider the hardware first.

Hardware

Major hardware components include the central processing unit (CPU); main memory (MM), also called random access memory (RAM); input/output devices; and secondary storage. Some examples of input devices are the keyboard, mouse, and secondary storage. Examples of output devices are the screen, printer, and secondary storage. Let’s look at each of these components in greater detail.

Central Processing Unit and Main   Memory

The central processing unit is the ‘‘brain’’ of the computer and the single most expensive piece of hardware in a computer. The more powerful the CPU, the faster the computer. Arithmetic and logical operations are carried out inside the CPU. Figure 1-1(a) shows some hardware components.

FIGURE 1-1  Hardware components of a computer and main memory

Main memory, or random access memory, is connected directly to the CPU. All programs must be loaded into main memory before they can be executed. Similarly, all data must be brought into main memory before a program can manipulate it. When the computer is turned off, everything in main memory is lost.

Main memory is an ordered sequence of cells, called memory cells. Each cell has a unique location in main memory, called the address of the cell. These addresses help you access the information stored in the cell. Figure 1-1(b) shows main memory with some data.

Today’s computers come with main memory consisting of millions to billions of cells. Although Figure 1-1(b) shows data stored in cells, the content of a cell can be either a programming instruction or data. Moreover, this figure shows the data as numbers and letters. However, as explained later in this chapter, main memory stores everything as sequences of 0s and 1s. The memory addresses are also expressed as sequences of 0s and 1s.

SECONDARY  STORAGE

Because programs and data must be stored in main memory before processing and because everything in main memory is lost when the computer is turned off, information stored in main memory must be transferred to some other device for permanent storage. The device that stores information permanently (unless the device becomes unusable or you change the information by rewriting it) is called secondary storage. To be able to transfer information from main memory to secondary storage, these components must be directly connected to each other. Examples of secondary storage are hard disks, flash drives, floppy disks, ZIP disks, CD-ROMs, and tapes.

Input /Output Devices

For a computer to perform a useful task, it must be able to take in data and programs and display the results of calculations. The devices that feed data and programs into computers are called input devices. The keyboard, mouse, and secondary storage are examples of input devices. The devices that the computer uses to display results are called output devices. A monitor, printer, and secondary storage are examples of  output  devices.  Figure 1-2 shows some input and output     devices.

FIGURE 1-2   Some input and output devices

Software

Software are programs written to perform specific tasks. For example, word processors are programs that you use to write letters, papers, and even books. All software is written in programming languages. There are two types of programs: system programs and application programs.

System programs control the computer. The system program that loads first when you turn on your PC is called the operating system. Without an operating system, the computer is useless. The operating system monitors the overall activity of the computer and provides services. Some of these services include memory management, input/output activities, and storage management. The operating system has a special program that organizes secondary storage so that you can conveniently access information.

Application programs perform a specific task. Word processors, spreadsheets, and games are examples of application programs. The operating system is the program that   runs  application programs.

The Language of a Computer

When you press A on your keyboard, the computer displays A on the screen. But what is actually stored inside the computer’s main memory? What is the language of the computer? How does it store whatever you type on the keyboard?

Remember that a computer is an electronic device. Electrical signals are used inside the computer to process information. There are two types of electrical signals: analog and digital. Analog signals are continuous wave forms used to represent such things as sound. Audio tapes, for example, store data in analog signals. Digital signals represent information with a sequence of 0s and 1s. A 0 represents a low voltage, and a 1  represents a high voltage. Digital signals are more reliable carriers of information than analog signals and can be copied from one device to another with exact precision. You might have noticed that when you make a copy of an audio tape, the sound quality of the copy is not as good as the original tape. On the other hand, when you copy a CD, the copy is as good as the original. Computers use digital  signals.

Because digital signals are processed inside a computer, the language of a computer, called machine language, is a sequence of 0s and 1s. The digit 0 or 1 is called a binary digit, or bit. Sometimes a sequence of 0s and 1s is referred to as a binary code or a binary number.

Bit: A binary digit 0 or 1.

A sequence of eight bits is called a byte. Moreover, 210  bytes = 1024 bytes is called           a kilobyte (KB). Table 1-1 summarizes the terms used to describe various numbers         of bytes.

TABLE 1-1   Binary Units

Unit	Symbol	Bits/Bytes
Byte		8 bits
Kilobyte	KB	210 bytes ¼ 1024  bytes
Megabyte	MB	1024 KB ¼ 210 KB ¼ 220 bytes ¼ 1,048,576 bytes
Gigabyte	GB	1024 MB ¼ 210 MB ¼ 230 bytes ¼ 1,073,741,824 bytes
Terabyte	TB	1024 GB ¼ 210 GB ¼ 240 bytes  ¼ 1,099,511,627,776 bytes
Petabyte	PB	1024 TB ¼ 210 TB ¼ 250 bytes   ¼ 1,125,899,906,842,624 bytes
Exabyte	EB	1024 PB ¼ 210 PB ¼ 260 bytes   ¼ 1,152,921,504,606,846,976  bytes
Zettabyte	ZB	1024 EB ¼ 210 EB ¼ 270 bytes   ¼ 1,180,591,620,717,411,303,424  bytes

Every letter, number, or special symbol (such as * or {) on your keyboard is encoded as a sequence of bits, each having a unique representation. The most commonly used encoding scheme on personal computers is the seven-bit American Standard Code for Information Interchange (ASCII). The ASCII data set consists of 128 characters numbered 0 through 127. That is, in the ASCII data set, the position of the first character is 0, the position of the second character is 1, and so on. In this scheme, A is encoded as the binary number 1000001. In fact, A is the 66th character in the ASCII character code, but its position is 65 because the position of the first character is 0. Furthermore, the binary number 1000001 is the binary representation of 65. The character 3 is encoded as 0110011. Note that in the ASCII character set, the position of the character 3 is 51, so the character 3 is the 52nd character in the ASCII set. It also follows that 0110011 is the binary representation of 51. For a complete list of the printable ASCII character set, refer to Appendix C.

NOTE:The number system that we use in our daily life is called the decimal system, or base 10. Because everything inside a computer is represented as a sequence of 0s and 1s, that is, binary numbers, the number system that a computer uses is called binary, or base 2. We indicated in the preceding paragraph that the number 1000001 is the binary representation of 65. Appendix E describes how to convert a number from base 10 to base 2 and vice versa.

Inside the computer, every character is represented as a sequence of eight bits, that is, as a byte. Now the eight-bit binary representation of 65 is 01000001. Note that we added 0 to the left of the seven-bit representation of 65 to convert it to an eight-bit representa- tion. Similarly, the eight-bit binary representation of 51 is   00110011.

ASCII is a seven-bit code. Therefore, to represent each ASCII character inside the computer, you must convert the seven-bit binary representation of an ASCII character  to an eight-bit binary representation. This is accomplished by adding 0 to the left of the seven-bit ASCII encoding of a character. Hence, inside the computer, the character       A is represented as 01000001, and the character 3 is represented as   00110011.

There are other encoding schemes, such as EBCDIC (used by IBM) and Unicode, which is a more recent development. EBCDIC consists of 256 characters; Unicode consists of 65,536 characters. To store a character belonging to Unicode, you need   two bytes.

The Evolution of Programming Languages

The most basic language of a computer, the machine language, provides program instructions in bits. Even though most computers perform the same kinds of operations, the designers of the computer may have chosen different sets of binary codes to perform the operations. Therefore, the machine language of one machine is not necessarily the same as the machine language of another machine. The only consistency among com- puters is that in any modern computer, all data is stored and manipulated as binary codes.

Early computers were programmed in machine language. To see how instructions are written in machine language, suppose you want to use the  equation:

wages  =  rate · hours

to calculate weekly wages. Further, suppose that the binary code 100100 stands for load, 100110 stands for multiplication, and 100010 stands for store. In machine language, you might need the following sequence of instructions to calculate weekly wages:

100100	010001
100110	010010
100010	010011

To represent the weekly wages equation in machine language, the programmer had to remember the machine language codes for various operations. Also, to manipulate   data, the programmer had to remember the locations of the data in the main memory. This need to remember specific codes made programming not only very difficult, but also error-prone.

Assembly languages were developed to make the programmer’s job easier. In assembly language, an instruction is an easy-to-remember form called a mnemonic. Table 1-2 shows some examples of instructions in assembly language and their corresponding machine language code.

TABLE 1-2  Examples of Instructions in Assembly Language and Machine Language

Assembly Language	Machine Language
LOAD	100100
STOR	100010
MULT	100110
ADD	100101
SUB	100011

Using assembly language instructions, you can write the equation to calculate the weekly wages as follows:

LOAD    rate MULT hours STOR               wages

As you can see, it is much easier to write instructions in assembly language. However,  a computer cannot execute assembly language instructions directly. The instructions first have to be translated into machine language. A program called an assembler translates the assembly language instructions into machine language.

Assembler: A program that translates a program written in assembly language into an equivalent program in machine language.

Moving from machine language to assembly language made programming easier, but   a programmer was still forced to think in terms of individual machine instructions. The next step toward making programming easier was to devise high-level languages that were closer to natural languages, such as English, French, German, and Spanish. Basic, FORTRAN, COBOL, Pascal, C, C++, C#, and Java are all high-level languages. You will learn the high-level language C++ in this  book.

In C++, you write the weekly wages equation as  follows:

wages  =  rate  *  hours;

The instruction written  in  C++  is  much  easier  to  understand  and  is  self-explanatory  to a novice user who is familiar with basic arithmetic. As in the case of assembly language, however, the computer cannot directly execute instructions written in a  high-level  language. To run on a computer, these C++ instructions first need to be translated into machine language. A program called a compiler translates instructions written in high- level languages into machine   code.

Compiler: A program that translates instructions written in a high-level language into the equivalent machine language.

Processing a C++ Program

In the previous sections, we discussed machine language and high-level languages and showed a C++ program. Because a computer can understand only machine language, you are ready to review the steps required to process a program written in   C++.

Consider the following C++  program:

#include   <iostream>

using  namespace   std;

int   main()

{

cout  <<  "My  first  C++  program."  <<  endl;

return  0;

}

At this point, you need not be too concerned with the details of this program. However, if you run (execute) this program, it will display the following line on the screen:

My first C++ program.

Recall that a computer can understand only machine language. Therefore, in order to run this program successfully, the code must first be translated into machine language. In this section, we review the steps required to execute programs written in   C++.

The following steps, as shown in Figure 1-3, are necessary to process a C++  program.

1.     You use a text editor to create a C++ program following the rules, or syntax, of the high-level language. This program is called the source code, or source program. The program must be saved in a text file that  has  the  extension  .cpp.  For  example,  if  you  saved  the  preceding program  in  the  file  named  FirstCPPProgram,  then  its  complete  name is  FirstCPPProgram.cpp.

Source program: A program written in a high-level    language.

2.     The C++ program given in the preceding section contains the statement

#include  <iostream>.  In a C++ program,  statements  that  begin  with the symbol # are called preprocessor directives. These statements are pro- cessed by a program called preprocessor.

3.     After processing preprocessor directives, the next step is to verify that the program obeys the rules of the programming language—that is, the program   is syntactically correct—and translate the program into the  equivalent  machine language. The compiler checks the source program for syntax errors and, if no error is found, translates the program into the equivalent machine language. The equivalent machine language program is called an object program.

Object program: The machine language version of the high-level language program.

4.     The programs that you write in a high-level language are developed using an integrated development environment (IDE). The IDE contains many programs that are useful in creating your program. For example, it contains the necessary code (program) to display the results of the program and several mathematical functions to make the programmer’s job somewhat easier. Therefore, if certain code is already available, you can use this code rather than writing your own code. Once the program is developed and successfully compiled, you must still bring the code for the resources used from the IDE into your program to produce a final program that the computer can execute. This prewritten code (program) resides in a place called the library. A program called a linker combines the object program with the programs from libraries.

Linker: A program that combines the object program with other programs in the library and is used in the program to create the executable  code.

5.     You must next load the executable program into main memory for execu-  tion. A program called a loader accomplishes this   task.

Loader: A program that loads an executable program into main memory.

6.    

The final step is to execute the program.

Figure 1-3 shows how a typical C++ program is processed.

As a programmer, you need to be concerned only with Step 1. That is, you must learn, understand, and master the rules of the programming language to create source programs.