 | It is software
(i.e., the instructions you write to perform actions and make decisions)
that controls computers (often referred to as hardware).
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| ANSI
C is the version of the C Programming language standardized
in 1989 in both the United States through the American National Standards
Institute (ANSI), and around the world through the International Standards
Organization (ISO).
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| Computers that might have filled large rooms and cost millions of dollars
25 years ago can now be inscribed
on the surfaces of silicon
chips smaller that a fingernail, and that cost perhaps a few
dollars each.
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| Approximately 150 million general-purpose computers are in use
worldwide helping people in business, industry, government,
and in their personal lives. That number could easily double in a few years.
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| A computer is a device capable of performing
computations and making logical decisions at speeds millions,
and even billions, of times faster than human beings can.
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| Computers process data under the control of computer
programs.
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| The various devices (such as the keyboard, screen, disks, memory, and processing
units) that comprise a computer system are referred to as hardware.
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The computer programs that run on a computer are referred to as software.
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The input unit
is the "receiving" section of the computer. Most information is entered
into computers today through typewriter-like keyboards.
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The output unit
is the "shipping" section of the computer. Most information is output from
computers today by displaying it on the screen or by printing it on paper.
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Thememory unit
is the "warehouse" section of the computer, and is often called either
memory or primary memory.
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The arithmetic and logic unit (ALU)
performs calculations and makes decisions.
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The Central Processing Unit (CPU)
is the computer's coordinator and is responsible for supervising the operation
of the other sections.
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Programs or data not actively being used by the other units are normally
placed on secondary
storage devices (such as disks) until they are again needed.
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In single-user
batch processing, the computer runs a single program at a time
while processing data in groups or batches.
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| Multiprogramming
involves the "simultaneous" operation of many jobs on the computer--the
computer shares its resources among many jobs.
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| Timesharing
is a special case of multiprogramming in which users access the computer
through terminals. The users appear to be running simultaneously.
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With distributed
computing, an organization's computing is distributed via networking
to the sites at which the real work of the organization is performed.
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File servers store programs and data that may be shared by client computers
distributed throughout the network, hence the termclient/server
computing.
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Any computer can directly understand only its own machine
language.
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Machine languages generally consist of strings of numbers (ultimately reduced
to 1s and 0s) that instruct computers to perform their most elementary
operations one at a time. Machine languages are machine-dependent. |
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English-like abbreviations form the basis of assembly
languages. Assemblers translate assembly language programs into
machine language.
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Compilers
translate high-level language programs into machine language.High-level
languages contain English words and conventional mathematical
notations.
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C is known as the development language of theUNIX
operating system.
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It is possible to write programs in C that
are portable to most computers.
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The ANSI C
standard was approved in 1989.
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FORTRAN
(FORmula
TRANslator) is used for mathematical applications.
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COBOL
(Common Business Oriented Language) is used primarily for commercial applications
that require precise and efficient manipulation of large amounts of data.
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Structured
programming is a disciplined approach to writing programs that
are clear, demonstrably correct, and easy to modify.
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Pascal
was designed for teaching structured programming in academic environments.
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Ada
was developed under the sponsorship of the United States Department of
Defense (DOD) using Pascal as a base.
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Ada multitasking allows
programmers to specify parallel activities.
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All C systems
consist of three parts: the environment,
the
language, and the standard
libraries.
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Library functions
are not part of the C language itself; these functions perform operations
such as input/output and mathematical calculations.
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C programs typically go through six
phases to be executed: edit, preprocess,
compile, link, load, and execute.
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The programmer types a program with an editor,
and makes corrections if necessary.
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The C preprocessor
obeys preprocessor directives which typically indicate that other files
are to be included in the file to be compiled, and special symbols are
to be replaced with program text.
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A compiler
translates a C program into machine language code (or object code).
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A linker links
the object code with the code for missing functions to produce an executable
image (with no missing pieces).
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A loader takes
an executable image from disk and transfers it to memory.
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A computer, under the control of the CPU, executes
a program one instruction at a time.
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Certain C functions (such as scanf) take their input from stdin
(the standard input device) which is normally assigned to the keyboard.
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Data is output to stdout
(the standard output device) which is normally the computer screen.
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There is also a standard error device referred to asstderr.
The stderr device (normally the screen) is used fordisplaying error messages.
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Although it is possible to write portable programs, there are many problems
between different C implementations and different computers that can make portability
difficult
to achieve.
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Concurrent
C is a C superset that includes capabilities for specifying
that multiple activities can be performed in parallel.
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C++
provides capabilities to do object-oriented programming.
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Objects
are essentially reusable software components that model items in the real
world.
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It is widely believed that C++ will become the dominantsystems
implementation language in the mid-to-late 1990s.
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