cosc175 - lec11 overview history hardware software software development life cycle programming...
TRANSCRIPT
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Overview
• History• Hardware• Software• Software Development Life Cycle• Programming Languages• Structured Programming• Defining the Problem
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History of computers• First Generation computers (1951-1958)
– vacuum tubes– used large amounts of electricity, heat,large and expensive– 1946 - ENIAC - computed trajectories for U.S. Army– 1951 - UNIVAC - first commercially available computer,
census• Second Generation computers (1959-1963)
– transistors, less heat– more reliable, less expensive
• Third Generation computers (1964-1970)– integrated circuits– less heat, higher speed
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History of computers• Fourth Generation computers (1971-present)
– microprocessor => Personal Computer– Apple II (1977), IBM PC (1981)– ARPANET (1969)– WWW (1991)– Today - cheaper, smaller, better
• Fifth Generation computers (present and beyond)– Artificial Intelligence
• http://www.history.com/shows/modern-marvels/videos/who-invented-the-computer#who-invented-the-computer
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Computer Components(Hardware)
Arithmetic Logic Unit
Control Unit
Auxiliary StorageDevice
Memory Unit ( RAM & Registers )
Central Processing Unit ( CPU ) Input Device
Output Device
Peripherals
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Software
• Systems Software– Operating System – software that
controls overall operation of computer– DOS, Windows, Unix, Linux
• Programming Environment– Editor/Compiler/Interpreter/Linker/ Debugger
• Application Software
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Software Development Life Cycle
1. Define the Problem (Analysis)2. Design the Solution
(Algorithm)3. Code Solution (Program)4. Test and Debug5. Maintain & Document
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1. Analysis
What? Defining the Problem Requirements Generate and document a clear problem
statement Need to talk to all stakeholders Most common cause of software system
failure traced to poor requirements gathering
IPO
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2. Design • HOW? • Planning• Algorithm – expansion of steps in
the IPO diagram• Flowchart• Pseudocode
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Start
Input payRate
Input hrsWorked
netPay = payRate * hrsWorked
Output netPay
Stop
Pseudocode:
Input payRateInput hrsWorkednetPay = payRate * hrsWorkedOutput netPay
Design tools
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pseudocode flowchart•Can be done easily on word processor•Implements structured•design elements well•Not visual•No standard
•Standardized•visual•Difficult to modify•requires special software to do on computer
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An Algorithm is . . .• Step-by-step procedures for solving a problem in a
finite amount of time. • We are learning to write algorithms and the
computer is simply a fast and flexible tool for implementing algorithms.
• An algorithm is an ordered set of instructions such that: (1) There are a finite number of steps. (2) It takes a finite amount of time to execute the steps. (3) Each step is precise in meaning, and “doable.” (4) It solves a general class of problems.
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3. Code the Solution
• Choose language• Edit – create source program• Compile - translate
– Syntax error – violate rules of programming language
• Link• Create an executable program
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4. Test and Debug
• Test with variety of data• Debugging: locating and correcting
errors– Logic error or bug - flaw in algorithm
• Run-time error e.g. Divide by zero
• Programming packages usually have debugger software to help programmer
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5. Maintain and Document
• Maintenance – Changing and maintaining existing programs– Most coding is actually maintenance
• Documentation – sometimes done by technical writers
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A Tempting Shortcut?
GOAL
THINKINGCODE
REVISEREVISE
REVISEDEBUG
DEBUG
DEBUG
TEST
CODEShortcut?
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Programming Languages• Definition: languages with strict grammar rules, symbols, and
words used to construct a computer program• Machine Languages
– is not portable, runs only on specific type of computer– is made up of binary-coded instructions (strings of 0s and 1s) – is the language that can be directly used by the computer
• Assembly Language– Mnemonic codes are used for the op. codes instead of binary,
EXA: LDA N, SUB B– assembly language program must be translated into machine
language before it can be executed, ‘assembler’.• High Level Languages
– portable– similar to natural language– Requires compiler – translates high-level language into
machine code– FORTRAN, Visual BASIC, COBOL, Pascal, Ada, C++, Java– most are standardized by ISO/ANSI
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C++• 1972 : C created by Dennis Ritchie at Bell Labs
=> 90% of UNIX is then written in C• 1983: C++ - Bjarne Stroustrup at Bell Labs • 1998 : ISO/ANSI standardization of C++• general-purpose programming language - many
uses• Flexible - few restrictions• high demand for C,C++ programmers• high level/low level• Portable - leader in portability• programmer oriented-"written by a professional
programmer for professional programmers"
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1. Edit: write and type the program (source code) in C++ , Save as myProg.cpp2: Compile: translate the source code into machine language => myprog.obj
syntax error – violation of the rules of the language. 3: Link = bring in other code from libraries, bind the modules together, etc => myProg.exe4: Run = run the executable file
Logic errors (bug) – An error caused by a mistake in programming instructions.A logic error causes a program to operate wrongly or produce incorrect data, but not to stop working
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Structured Programming
Top-down Design– divide and conquer
Modularity subprograms Stepwise refinement
The Structure Theorem- Use 3 basic control structures to solve any problem
1. Sequence2. Selection (if-then-else)3. Repetition (loop)
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SEQUENCEStatement
Statement
Statement
Display “Enter Name”Input nameDisplay “Hello “ name
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SELECTION (branch)IF Condition THEN Statement1 ELSE Statement2
Statement1 Statement
Statement2
Condition . . .
True
False
If (num > 0) Display “Positive”Else Display “Negative”
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LOOP (repetition)
Statement
Condition. . .
False
True
WHILE Condition DO Statement1
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SUBPROGRAM (function)
SUBPROGRAM1 . . .
SUBPROGRAM1 a meaningful collection of SEQUENCE, SELECTION, LOOP, SUBPROGRAM
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Computing Profession Ethics
• copy software only with permission from the copyright holder
• give credit to another programmer by name whenever using his/her code
• use computer resources only with permission
• guard the privacy of confidential data• use software engineering principles to
develop software free from errors
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As proposed by the project sponsor.
As specified in the project request.
As designed by the senior analyst.
As produced by the programmers.
As installed at the user's site. What the user wanted.
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Step 1:AnalysisDefine the Problem
IPO1. Input: Determine what is given
=>nouns, adjectives
2. Output: Determine what is required =>nouns, adjectives
3. Processing: Determine the transformations needed,actions needed to produce the required output=>verbs, adverbs
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variables
• Input and output data• Nouns• Naming convention
– No spaces– Meaningful names– Usually begin with lowercase– Examples: roomWidth, numPeople,
studentName
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Example 1
Input
Processing
Output
Read three numbers, add them together and print the total.
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1. Identify inputsUnderline nouns
Input
Processing
Output
Read three numbers, add them together and print the total.•Break up several values into separate variables
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1. Identify inputsfill Input column first
Input
Processing
Output
num1
num2
num3
Read three numbers, add them together and print the total.•Break up several values into separate variables
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2. Identify outputsoutput column next
Input
Processing
Output
num1
total
num2
num3
Read three numbers, add them together and print the total.•Break up several values into separate variables•No verbs here
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3. Processing-Define processing steps by bolding verbs
Input
Processing
Output
num1
total
num2
num3
Read three numbers, add them together and print the total.
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Each verb is a process step
Input
Processing
Output
num1
Read num1, num2, num3
total
num2
Calculate total
num3
Display total
Read three numbers, add them together and print the total.Hint: Usually follows: input, process, output
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Step 3: define list of actions
Input
Processing
Output
num1
Read num1,num2,num3
total
num2
Add numbers together
num3
Print total
Read three numbers, add them together and print the total.•Hint: Use verbs•these steps usually involve the input and output defined in step 1
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Example 2:
Input
Processing
Output
maxTemp avgTemp
minTemp
Write a program to prompt the operator for the maximum and minimum temperature readings on a particular day, accept those readings as integers, and calculate and display on the screen the average temperature.
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Example 2:
Input
Processing
Output
Write a program to prompt the operator for the maximum and minimum temperature readings on a particular day, accept those readings as integers, and calculate and display on the screen the average temperature.
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Example 2:
Input
Processing
Output
maxTemp Prompt for maxTemp,minTemp
avgTemp
minTemp
Calculate avgTemp
Display avgTemp
Write a program to prompt the operator for the maximum and minimum temperature readings on a particular day, accept those readings as integers, and calculate and display on the screen the average temperature.