Computer Program - Revision history

DavidB4-bot: /* An Example */Spelling/Grammar Check & Cleanup, typos fixed: sentance → sentence (2)

2016-06-28T13:52:03Z

An Example: Spelling/Grammar Check & Cleanup, typos fixed: sentance → sentence (2)

DavidB4: category tweak (manual of style)

2016-03-31T13:12:17Z

category tweak (manual of style)

EdBot: Category:Computer Science

2008-04-01T21:32:56Z

Category:Computer Science

Ed Poor: /* Nature of Programs */

2007-08-11T02:07:00Z

Nature of Programs

Eac: New page: A '''Computer Program''' is a set of instructions for a computer to follow. Programs are written in Programming Languages. The written program is referred to as '''source code''' a...

2007-06-29T21:10:44Z

New page: A '''Computer Program''' is a set of instructions for a computer to follow. Programs are written in Programming Languages. The written program is referred to as '''source code''' a...

New page

A '''Computer Program''' is a set of instructions for a computer to
follow. Programs are written in [[Programming Language]]s. The written
program is referred to as '''source code''' and is converted into a form
that a [[computer]] can execute via another program, called an
'''interpreter''', '''translator''', '''compiler''', or '''assembler'''.
Programs are also referred to as [[software]], whereas the computer
that executes them is called '''hardware'''. If the program is stored in
a hardware device (such as in a read-only memory chip), the program/device combination is called '''firmware'''.

All useful work that a computer does is controlled by one or more
programs, including the [[Operating System]] (O/S) which is a program
that controls other programs. Other examples of programs: video games,
Microsoft Word, Internet Explorer, and email viruses.

==Nature of Programs==
Programs are executed by the computer's [[CPU]], and all source code must
ultimately be translated into the '''machine code''' instructions for the
CPU before it can be executed. Each instruction performs one specific
small task in the CPU hardware. The CPU executes the instructions one at
a time, from start to finish. Most instructions perform some operation
on some data. For instance, an instruction may add two numbers together.
Another instruction may output the result. The most powerful feature of
computer programs is the ability to choose what instructions to execute
based on a comparison of data. This '''conditional execution''' allows
very complex programs to be written.

High-level programming languages, such as the [[BASIC Programming
Language]], allow a programmer to write his program using higher-level
concepts. A single '''statement''' in a programming language may
translate into hundreds of machine code instructions. Most programs are
therefore written using a high-level programming language and most
programmers think in terms of the '''abstraction''' provided by that
language.

There are five basic aspects of programs: '''data''' is information that
is processed and/or generated by the program. Data includes text,
numbers, measurements, and inputs to the program. '''algorithms''' are
the steps to follow to accomplish a given task, which are implemented as
a series of instructions. Also called '''routines'''. Algorithms operate on data. For instance, an algorithm may calculate the square-root of a number or count the number
of letters in a word. '''I/O''' means Input/Output. Input is the
process of taking data from outside the program, and output is when the
program sends data to the user or stores it somewhere outside of the
program (such as on a hard disk). '''Flow control''' is the ability to
choose what code is executed. This involves changing the order in which
instructions are executed. If the change is based on certain values of
data, it is called '''conditional''' execution. When the same
instructions are repeated it is referred to as a '''loop'''. Finally,
'''subroutines''' are algorithms that are used in multiple places in the
program but not in a way that can be made use of via a loop. Rather than
include a copy of the algorithm at every place it is needed, it is
included once and the program can make '''calls''' to the algorithm. All
programs involve some combination of these five aspects of programs.

'''Bugs''' are flaws in programs that cause them to operate in a manner
not intended by the programmer. The misbehavior may be serious or minor.
The larger a program, the greater the chance of the existance of bugs, and the greater the number of different bugs.
The quality of a program is sometimes measured in terms of lines of code per
bug.

The speed of a program depends upon how many instructions are needed to
accomplish its tasks, the speed of the CPU running the program, and the
speed of the I/O. An inefficiently coded program takes more instructions
to do a unit of work than an efficiently coded program, and will
therefore run more slowly. However, inefficiency is sometimes purposely
chosen if the inefficiency leads to a simpler implementation. Note that in a multi-tasking environment, such as Microsoft Windows, the speed of a program can also be affected by the execution of other programs.

==An Example==
A program can be viewed as the process of obtaining some data, performing
operations on the data, and outputting the results. When combined with
flow control, the program can monitor something's status, and
appropriately respond to changes in that status. For instance, a word
processing program (such as Microsoft Word) will wait for the user to
type a character on the keyboard. This '''wait''' is a loop that
continuously checks for a typed character. When the character is typed,
the character becomes the data. The program will then perform some
operations depending upon what character was typed. For instance, there
may be an algorithm to automatically convert the character to uppercase
if the user is positioned at the start of a sentance. This is
conditional execution ('''if''' the character is a lowercase letter
'''and''' at the start of a sentance). Next the program outputs the
character (perhaps changed from the original data) to the screen where
the user sees it. Finally, the program loops back to the start to wait
for another character.

[[Category:Information technology]]
[[Category:computer science]]

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 operations depending upon what character was typed.  For instance, there
 may be an algorithm to automatically convert the character to uppercase
-if the user is positioned at the start of a sentance.  This is
+if the user is positioned at the start of a sentence.  This is
 conditional execution ('''if''' the character is a lowercase letter
-'''and''' at the start of a sentance).  Next the program outputs the
+'''and''' at the start of a sentence).  Next the program outputs the
 character (perhaps changed from the original data) to the screen where
 the user sees it.  Finally, the program loops back to the start to wait

@@ Line 55: / Line 55: @@
 '''Bugs''' are flaws in programs that cause them to operate in a manner
 not intended by the programmer.  The misbehavior may be serious or minor.
-The larger a program, the greater the chance of the existance of bugs, and the greater the number of different bugs.
+The larger a program, the greater the chance of the existence of bugs, and the greater the number of different bugs.
 The quality of a program is sometimes measured in terms of lines of code per
 bug.
@@ Line 65: / Line 65: @@
 therefore run more slowly.  However, inefficiency is sometimes purposely
 chosen if the inefficiency leads to a simpler implementation.  Note that in a multi-tasking environment, such as Microsoft Windows, the speed of a program can also be affected by the execution of other programs.
 ==An Example==