Computer Programming
CONTENTS
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Introduction to Operating Systems
Introduction to programming languages
Introduction to perl programming language
Programming skills in perl
Perl applications in bioinformatics
Software Categories
• System SW
– Programs written for computer systems
• Compilers, operating systems, …
• Application SW
– Programs written for computer users
• Word-processors, spreadsheets, & other
application packages
Operating system
• The set of software that controls the overall
operation of a computer system, typically by
performing such tasks as memory allocation, job
scheduling, and input/output control
• Software designed to control the hardware of a
specific data-processing system in order to allow
users and application programs to make use of it.
OS Tasks
The operating system's tasks, in the most
general sense, fall into six categories:
i.
ii.
iii.
iv.
v.
vi.
Processor management
Memory management
Device management
Storage management
Application interface
User interface
Language
• The purpose of language is simply that it
must convey meaning. (Confucius)
• That which can be said, can be said clearly.
(Wittgenstein,1963)
• A program is a specification of a computation.
A programming language is a notation for
writing programs.(Sethi,89)
What is a programming language?
• A language that is intended for the expression
of computer programs and that is capable of
expressing any computer program.
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What is Programming
• Program – a very specific set of instructions (or
command lines) that making a computer do what
you want it to do
• Programming – the process of creating a program
– the development of a solution to an identified program,
and setting up of a related series of instructions which,
when directed through computer hardware, will produce
the desired results
Differences or Similarities
• Natural Language
– Grammar
– Vocabulary
– Sentences
• Programming Language
– Syntax
– Objects, data types
– Commands
Steps in program development
1.
2.
3.
4.
5.
Define the problem
Outline the solution(pseudocode)
Develop the outline into an algorithm
Test the algorithm for correctness
Code the algorithm into a specific
programming language
6. Run the program on the computer
7. Document and maintain the program
Define the Problem
• Divide the problem into three components
(called IPO):
– Inputs – what do you have?
– Outputs – what do you want to have?
– Processing
• how do you go from inputs to outputs?
• A defining diagram is recommended
Outline the Solution
• The major processing steps involved
• The major subtasks (if any)
• The major control structures (e.g. repetition loops)
• The major variables and record structures
• The mainline logic
Develop the Outline into an Algorithm
• Algorithm is a set of precise steps that
describe exactly the tasks to be performed,
and the order in which they are to be carried
out
• Pseudocode (a form of structured English) is
used to represent the solution algorithm
Test the Algorithm for Correctness
• The main purpose of desk checking the algorithm is
to identify major logic errors early, so that they may
be easily corrected
• Test data needs to be walked through each step in
the algorithm, to check that the instructions
described in the algorithm will actually do what they
are supposed to
Code the Algorithm into a Specific
Programming Language
• Only after all design considerations have been met
should you actually start to code the program into
your chosen programming language (e.g. Visual
Basic, Java, C++)
Run the Program on the Computer
• This step uses a program compiler and programmerdesigned test data to machine test the code for
syntax errors
• Program complier translate high-level languages (e.g.
VB) to low-level machine language before execution
Document and Maintain the Program
• Not the last step in the program development
process
• An ongoing task from the initial definition of the
problem to the final test result
• Involves both external documentation (such as
hierarchy charts) and internal documentation that
may have been coded in the program
How do Programming Languages Differ?
Common Constructs:
• basic data types (numbers, etc.); variables;
expressions; statements; keywords; control
constructs; procedures; comments; errors ...
Uncommon Constructs:
• type declarations; special types (strings, arrays,
matrices, ...); sequential execution; concurrency
constructs; packages/modules; objects; general
functions; generics; modifiable state; ...
Pseudocode vs Algorithm
• Pseudocode is a compact and informal high-level description of a
computer programming algorithm that uses the structural
conventions of some programming language, but is intended for
human reading rather than machine reading.
• Algorithm Procedure that produces the answer to a question or the
solution to a problem in a finite number of steps. In mathematics,
computing, and related subjects, an algorithm is a sequence of
finite instructions, often used for calculation and data processing. It
is formally a type of effective method in which a list of well-defined
instructions for completing a task will, when given an initial state,
proceed through a well-defined series of successive states,
eventually terminating in an end-state.
Problem 1

A program is required to read
three numbers, add them
together and print their
total.
• Defining diagram
Input
Number1
Number2
Number3
Processing
Prompt for input
numbers
Get input numbers
Apply addition
Display total
Output
total
Solution Pseudocode
Begin Program
Get number1
Get number2
Get number3
Total = number1 + number2 + number3
Display total
End Program
Problem 2
• A program is required to prompt the
terminal operator for the maximum
and minimum temperature readings on
a particular day, accept those
readings as integers, and calculate
and display to the screen the
average temperature, calculated by
(maximum temperature + minimum
temperature)/2.
• Defining diagram
Input
Max_temp
Min_temp
Processing
Output
Prompt for temperatures
Avg_temp
Get temperatures
Calculate average temperature
Display average temperature
Solution Pseudocode
Begin program
Get max_temp, min_temp
Avg_temp= (max_Temp + min_temp)/2
Output avg_temp to the screen
End Program
Problem 3
• Calculate the circumference and
area of a circle
• Defining diagram
Input
Radius
pi
Processing
Output
Get radius, pi
Circumfere
Calculate circumference = 2 * P nce
I* radius
Calculate
2
area=PI * radius ^
Display circumference, area
area
Solution Pseudocode
Begin program
get radius, PI
circumference = 2 * P I* radius
area=PI * radius * radius
display circumference, area
End program
Attributes of a good language
1. Clarity, simplicity, and unity
– Have a minimum number of different concepts, with the
rules for their combination, simple and regular (conceptual
integrity).
– readability
2. Orthogonality
– Being able to combine various features of a language in all
possible combinations.
3. Support for abstraction
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Attributes of a good language
4. Ease of program verification
– Proof of correctness, desk checking, test
– Simplicity of semantic and syntax
5. Programming environment
6. Portability of programs
7. Cost of use
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Program execution
Program translation
Program creation, testing, and use
Program maintenance
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Attributes of a good language (another
view: to make a software reliable, maintainable, efficient)
• Reliability
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–
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Writability
Readability
Simplicity
Safety (no goto, no pointers)
Robustness (undesired events can be trapped, like
arithmetic overflow, invalid inputs)
• Maintainability
– Factoring (modularity)
– Locality
• Efficiency
Jazayeri
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Can you answer these questions?
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What is an OS?
PL?
Pseudocode vs Algorithm?
Steps involved in programming?
Attributes of good PL?
How do PL differ?
Write pseudocode for a given problem?
Assignment
• Uses of internet as biologists
• Single page