An Overview of Computers
and Programming
1
Understanding Computer Systems
Computer system
• Combination of all the components required to
process and store data using a computer
• Made up of
• Hardware
• Software
Hardware
• Equipment associated
Software
• Computer instructions
• Tells the hardware what to do
• Named Programs
2
Programs
Instructions
written by
programmers
Application
System
software such
software
as word
programs
processing,
managing
spreadsheets,
operating
payroll and
systems like
inventory,
Windows,
even games Linux, or UNIX
Computer hardware and software
manage three major operations :
Input
Data items such as text, numbers, images, and
sound
Processing
Calculations and comparisons performed by the
central processing unit (CPU)
Output
Resulting information that is sent to a printer, a
monitor, or storage devices after processing
Computer Terminology
Programming language
Syntax
• Used to write computer
instructions (program code)
• Examples
• Visual Basic, C#, C++, or
Java
• Rules governing word usage
and punctuation
Computer memory
Permanent storage
devices
• Computer’s temporary, internal
storage – random access
memory (RAM)
• Volatile memory – lost when
the power is off
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Nonvolatile memory
Hard drives
Flash drives
CD
Computer Terminology
Compiler or interpreter
• Translates source code into
machine language (binary
language) statements called
object code
• Checks for syntax errors
Program executes or
runs
• Input will be accepted, some
processing will occur, and
results will be output
Users or end users
Documentation
• People for whom a program
is written
• Supporting paperwork for a
program
Computer Terminology
Syntax errors
Logical errors
• Programs with syntax
errors cannot execute
• Errors in program logic
produce incorrect
output
Logic of the
computer program
Variable
• Sequence of specific
instructions in specific
order
• Named memory
location whose value
can vary
Program Development
Understand the problem
Plan the logic
Code the program
Use software (a compiler
or interpreter) to translate
the program into machine
language
Test the program
Put the program
into production
Maintain the program
Understanding the Problem
Print a list of all employees who
have been here for over five years
Does the director want a list of full-time employees only, or a list of full- and
part-time employees together?
Does she want to include people who have worked for the company on a
month-to-month contractual basis over the past five years, or only regular,
permanent employees?
Do the listed employees need to have worked for the organization for five years as of
today, as of the date of the dinner, or as of some other cutoff date?
What about an employee who worked three years, took a two-year leave of absence,
and has been back for three years?
What data should be included for each listed employee? Should the list contain both
first and last names? Social Security numbers? Phone numbers? Addresses?
Should the list be in alphabetical order? Employee ID number order? Length-ofservice order? Some other order?
9
Planning the Logic
n
n
Heart of the programming process
Most common planning tools
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n
Flowcharts
Pseudocode
IPO charts (input, processing, and output)
TOE charts (tasks, objects, and events)
Desk-checking
– Walking through a program’s logic on paper
before you actually write the program
10
Code the Program
n
Hundreds of programming languages
available
– Choose based on features
– Similar in their basic capabilities
n
Easier than the planning step
11
Using Software to Translate the
Program into Machine Language
n
Translator program
– Compiler or interpreter
– Changes the programmer’s English-like highlevel programming language into the low-level
machine language
n
Syntax error
– Misuse of a language’s grammar rules
– Programmer corrects listed syntax errors
– Might need to recompile the code several times
12
Using Software to Translate the
Program into Machine Language
13
Testing the Program
n
Logical error
– Results when a syntactically correct statement, but
the wrong one for the current context, is used
n
Test
– Execute the program with some sample data to
see whether the results are logically correct
n
n
Debugging is the process of finding and
correcting program errors
Programs should be tested with many sets of
data
14
Putting the Program into
Production
Process depends on
program’s purpose
• May take several months
The entire set of actions an
organization must take to
switch over to using a new
program or set of programs
15
Maintaining the Program
Maintenance
• Making changes after
the program is put into
production
Common first
programming job
• Maintaining previously
written programs
Make changes to
existing programs
• Repeat the
development cycle
16
Understanding Programming
and User Environments
Many options for programming and user environments :
Planning
• Flowchart
• Pseudocode
Coding
• Plain text editor
• Text editor that is part of an integrated development environment (IDE)
Executing
• Input from keyboard, mouse, microphone
Outputting
• Text, images, sound
Understanding Programming
Environments (continued)
18
Understanding User
Environments
• Command line
• Location on your computer screen where
you type text entries to communicate with
the computer’s operating system
• Graphical user interface (GUI)
• Allows users to interact with a program in
a graphical environment
Understanding User
Environments (continued)
20
Understanding User
Environments (continued)
21
Understanding the Evolution
of Programming Models
n
n
People have been writing modern computer
programs since the 1940s
Newer programming languages
– Look much more like natural language
– Are easier to use
– Create self-contained modules or program
segments that can be pieced together in a variety
of ways
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Major models or paradigms
used by programmers
Understanding the Evolution
of Programming Models
Procedural programming
Focuses on the procedures that
programmers create
Object-oriented programming
Focuses on objects, or “things,”
and describes their features (or
attributes) and their behaviors
23
Review - True or False
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Hardware is the equipment, or the devices, associated with a computer. Software is
computer instructions.
The grammar rules of a computer programming language are its syntax.
You write programs using machine language, and translation software converts the
statements to a programming language.
The oldest computer programs were written in many separate modules.
Procedural programmers focus on actions that are carried out by a program.
Object-oriented programmers focus on a program’s objects and their attributes and
behaviors.
You can type a program into an editor that is part of an integrated development
environment, but using a plain text editor provides you with more programming help.
When a program runs from the command line, a user types text to provide input.
Although GUI and command-line environments look different, the logic of input, processing,
and output apply to both program types.
Understanding the problem that must be solved can be one of the most difficult aspects of
programming.
The two most commonly used logic-planning tools are flowcharts and pseudo code.
Flowcharting a program is a very different process if you use an older programming
language instead of a newer one.
A program with syntax errors can execute but might produce incorrect results.
Although the syntax of programming languages differs, the same program logic can be
expressed in different languages.
Most simple computer programs include steps that perform input, processing, and output.