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DEE 2112 Sem 1 09/10
CHAPTER 1
PRINCIPLE OF SOFTWARE DEVELOPMENT
DEE 2112 Sem 1 09/10
Objectives
In this chapter you will learn:
The computer programming languageTo solve problem using problem-solving strategies
and methodsThe algorithm as a guidance in designing program
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SOFTWARE DEVELOPMENT PRICIPLE
SubtopicsIntroduction to ProgrammingProblem Solving & Software Development
ApproachAlgorithm Representation
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1.1 Intro to Programming Programming is the core of everything to do with computers,
computing, networked systems, management information systems, multimedia and so on (all computer-based things)
Everything that runs on a computer is a program and somebody (programmer) has to write it using specific programming language. To understand how computers can be used, how applications work, how systems are configured, it is necessary for you to understand
what programs are and how they are constructed.
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1.2 Problem Statement & SDA
Problem Solving The process of transforming the description of
a problem into the solution of that problem by using our knowledge of the problem domain and by relying on our ability to select and use appropriate problem-solving strategies, techniques, and tools.
DEE 2112 Sem 1 09/10
Software Development Method
Requirements specification Analysis Design Coding & Implementation Testing & Verification Documentation & Maintenance
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Software Development Method
Requirements specification provides us with a precise definition of the problem.
In the analysis phase, we identify problem inputs, outputs, special constraints, and formulas and equations to be used.
The design phase is concerned with developing an algorithm for the solution of the problem.
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Software Development Method
Coding & ImplementationCode the finalized algorithm using a suitable
programming language.Go through the compiling & execution process.Normally, you will face this three types of
programming errorsLogic/Design errors Syntax errorsRuntime errors
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Logic/Design errorso Design errors occur during the analysis, design, and
implementation phases. o We may choose an incorrect method of solution for
the problem to be solved, we may make mistakes in translating an algorithm into a program, or we may design erroneous data for the program.
o Design errors are usually difficult to detect. o Debugging them requires careful review of problem
analysis, algorithm design, translation, and test data.
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Syntax Errors o Syntax errors are violations of syntax rules, which
define how the elements of a programming language must be written.
o They occur during the implementation phase and are detected by the compiler during the compilation process. In fact, another name for syntax errors is compilation errors.
o If your program contains violations of syntax rules, the compiler issues diagnostic messages.
o Depending on how serious the violation is, the diagnostic message may be a warning message or an error message.
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Runtime Errorso Run-time errors are detected by the computer while
your program is being executed. o They are caused by program instructions that require
the computer to do something illegal, such as attempting to store inappropriate data or divide a number by zero.
o When a run-time error is encountered, the computer produces an error diagnostic message and terminates the program execution.
o You can use diagnostic messages to debug run-time errors.
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Software Development Method
Documentation & MaintenanceFor every problem solving, there are 5 things to be documented
Program description Algorithm development and changes Well-commented program listing Sample test run User’s manual
Maintenance is concerned with ongoing correction of problems, revision to meet changing needs and addition of new features. The better the documentation is, the efficiently this phase can be performed.
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1.3 Algorithm Representation An algorithm is a sequence of a finite number of steps arranged in a specific logical order that, when executed, produces the solution for a problem. An algorithm design should be put on paper. For this purpose, and also to facilitate its development, we resort to pseudocoding and flowcharting
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Analogy
A) How to make a telephone call ?i. ?
ii) ? iii) ? B) How to make a fried rice ? C) How to buy a tin of pepsi-cola from vending machine ?
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Pseudocoding
Short English phrases with a limited vocabularyare use to describe the algorithm (the processing steps). A pseudocode must :
have a limited vocabulary be easy to learn produce simple, English-like narrative notation be capable of describing all algorithms, regardless
of their complexity
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Example of Pseudocode
Problem 1 : (Sequence structure) Compute total of resistor values.
Begin read resistor1 read resistor2 total = resistor1 + resistor2 print “ total “ End
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Flowcharting
A graphical technique for algorithm design and representation, is equivalent to pseudocoding and can be used as an alternative to it.
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Flowchart SymbolsSymbol Name Of Symbol Description And
Example
TerminalIndicates the beginning or end of an algorithm
Input/OutputIndicates an Input or Output operation
ProcessIndicates computation or data manipulation
DecisionIndicates a decision point in the algorithm
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Flowchart SymbolsSymbol Name Of Symbol Description And
Example
Loop
Specific for for statementIndicates the initial, final and increment values of a loop.
Flow Lines/ ArrowUsed to connect the symbols and indicates the logic flow
On-Page Connector Provides continuation of a logical path on another point in the same page.
Off-Page ConnectorProvides continuation of a logical path on another page
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Example of Flowchart
Problem 1 : (Sequence statements) Compute total of resistor values.
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Pseudocode & Flowchart Convention
Sequence Structureo a series of steps or statements that are executed
in order (ex : as shown in Problem 1)Selection Structure
o Define two courses of action depending on the outcome condition ( true or false)
Repetition control structures
o Specifies a block of one or more statements that are repeatedly executed until a condition is satisfied.
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Sequence Structure
begin
Statement_1
Statement_2
…
Statement_n
end
Statement_1
Statement_2
Statement_n
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Selection Structure• Single Selection (if)
if condition
statement
if condition
then_part
else
else_part
end_if
• Double Selection (if-else)
condition
if_partelse_part
YesNo
statementcondition
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Repetition Structure
while condition
loop-body
end_while condition Loop_bodyYes
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Applying the SDM ( Phase 1 to 3)
Problem : The C programming test scores can be
classified into two condition, PASS and FAIL. The student is require to input their marks in positive integer . If the score is greater than or equal 50 message Pass will appear, message Fail otherwise
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Applying the SDM
Phase 1 : Requirement Specification Selection Structure test scores, message ‘PASS’, message ‘FAIL’, greater or equal
to 50, less than 50
Phase 2 :Data requirements : Input : test_score Output : ‘PASS’ or ‘FAIL’ Relevant formula : test_score >= 50 test_score < 50 Constrain : the test score must greater than 0 (zero)
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Applying the SDM
Phase 3 : Design ( Pseudocode/Flowchart) Pseudocode
Begin Read the test scores Begin while while test_score < 0 Print ‘ Re-enter your score and must greater than 0’ Read the test_score End while if test_score >= 50 print ‘PASS’ else print ‘FAIL’End
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Applying the SDM
Flowchart
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Exercise
1. Write an algorithm that calculates the areas of a football field.
2. Write an algorithm that finds the smallest element among a, b, and c.