CptS 121 Fall 09 Lecture 12

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CptS 121 Fall 09 Lecture 1-2

• HK Chapter 1 Computer Software The Software
  Development Process
• Lecture Outline
• Computer Software (revisited)
• Programming Languages
• Software Development Method
• Example Application

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The Continuum of Programming Languages
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High-Level Programming Languages Developed for
Many Application Areas

• Scientific programming FORTRAN
• Business data processing COBOL
• Artificial Intelligence LISP, PROLOG
• Systems programming C (this course)
• Real-time distributed systems Ada
• GUIs, object-oriented programming SmallTalk
• Object-oriented programming C, Java, C

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High-Level languages Must Be Translated

• Problem Computers cant understand high-level
  programming languages
• Solution They must be translated
• Programmer uses a text editor to write a
  text-based source file in a programming language
• Compiler translates source file
• Checks to make sure that program is syntactically
  correct
• If so, the compiler translates the program into
• an object file with machine language
  instructions

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Object File Translated by Compiler Willll NOT
Execute

• High-level programs often make use of software
  libraries containing predefined pieces of code,
  including
• Math functions
• Input/output functions
• In order to execute, object file must be linked
  to object files containing these predefined
  pieces of code
• A Linker program performs this operation
• A Loader program loads the linked program into
  memory so that it can be executed

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Executing Programs Results in Interactive Program

• In this class, programs will execute in a
  text-based window called a console
• Input data can be entered at command-line prompts
• Output results will be displayed in the console
  window
• In the real world, most programs have a graphical
  user interface
• GUI programming is, however, beyond the scope of
  this course

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Integrated Development Environments Make
Programming More Accessible

• Combine compiler, linker, and loader with a
  source code editor
• Insulate programmers from the details of
  compiling, linking, and loading
• Provide a variety of tools to assist programmers,
  for example,
• Source code syntax highlighting
• Autocompletion lists ("Intellisense")
• A debugger, which allows a programmer to step
  through programs, one instruction at a time

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Software Development Method Provides Systematic
Approach

• Analogous to the Scientific Method in the
  sciences, and the Systems Approach in business
• Six basic steps
• Specify problem requirements
• Analyze the problem
• Design an algorithm to solve the problem
• Implement the algorithm
• Test and verify the completed program
• Maintain and update the program

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1.Specify Problem

• In the real world of analysis, problem
  specification is called requirements analysis,
  and it is one of the most difficult steps
• In this class, the problem will be given to you
  in a few sentences, or as a pseudocode algorithm
• Usually, there will be some sort of scenario to
  make the problem more concrete
• Exact inputs and outputs may not be specified,
  but should be inferable from the problem statement

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2. Analyze Problem

• Identify
• Inputs (input data to be processed)
• Outputs
• the results to be displayed and/or stored
  somewhere
• The format of the results
• Problem variables
• Formulas relating problem variables
• If problem specification and analysis are done
  wrong, youll solve the wrong problem

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Example of Problem Specification and Analysis

• Problem statement Calculate the temperature in
  degrees Celsius given the temperature in degrees
  Fahrenheit
• Problem Input
• FahrenheitTemp Temperature in degrees Fahrenheit
• Problem Output
• CelsiusTemp Temperature in degrees Celsius
• Formula
• CelsiusTemp 5/9 (FahrenheitTemp 32)

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3. Design Algorithm

• Can be the most challenging and creative part of
  the method
• Decompose the problem into high-level steps or
  subproblems (top-down design)
• Then figure out the details of solving each
  subproblem (algorithm refinement)
• Use pseudocode to write algorithms in this step
• General algorithm
• Get the data
• Perform the computations
• Display the results
• Desk check your algorithm
• Simulate its execution on sample input data
• Make sure that it works with the correct inputs,
  and produces the correct outputs

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4. Implement Algorithm

• Translate your pseudocode into a high-level
  programming language
• Remove all syntax errors from your program

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5. Test and Verify Completed Program

• Testing
• Perform code review on a team to identify issues
  with the code, e.g.,
• Does your implementation meet requirements?
• Is the code well documented?
• Does it adhere to good design principles?
• etc.
• Run your program with sample input data
• Verify that the outputs are correct
• Use a debugger to trace through your program and
  to pinpoint logic errors (debugging is an
  essential part of testing)

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6. Maintain Program

• Most programs are used for a long period of time
  (5 years or more)
• Previously undetected errors will emerge, and
  clients needs will change
• Maintenance will thus be required to keep the
  program up to date and working properly

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Documentation is an Important Part of Maintenance

• Programs often outlast the programmers who
  originally developed them
• It is therefore important to make it easy for new
  program team members to maintain a program
• Document, document, document!
• Comments are absolutely essential to reading and
  understanding someone elses code
• Adhere to established or accepted coding
  conventions and style
• Clever code that solves problems in
  unconventional ways is difficult to understand
  and maintain

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Applying the Software Development Method

• Warning You will rarely get it right the first
  time! This is an iterative process in which you
  would do well to be persistent and learn from
  your mistakes
• Example problem Compute a students quiz score
  average given three integer quiz scores.

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Step 2. Analyze Problem

• Problem inputscore1, score2, score3 (the three
  quiz scores)
• Problem outputaverage (the average of the three
  quiz scores)
• Relevant formulaaverage sum of scores/number
  of scores

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Step 3. Design the Algorithm

• Algorithm
• Get the three quiz scores
• Compute the average score
• Display the result
• Refined algorithm
• Get the three quiz scores
• Compute the average score
• Average (score1 score2 score3)/3
• Display the result

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Step 4. Implement the Algorithm

• Implementation (in C)/ Computes the average
  of three quiz scores /include ltstdio.hgt /
  printf, scanf defs /define NUM_SCORES 3int
  main(void)
• int score1, score2, score3 double
  average / Get the scores / printf("Enter
  quiz score 1 ") scanf("d", score1)
  printf("Enter quiz score 2 ") scanf("d",
  score2) printf("Enter quiz score 3 ")
  scanf("d", score3) / Compute average /
  average ((double)(score1 score2 score3))/
  ((double) NUM_SCORES)
  / Display result / printf("The average of
  those three scores is f.", average)
  return(0)

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Steps 5 and 6 Test and Maintain Program

• Testing
• This program is too small for a peer code review
  to be of much help
• We would compile and execute the program, trying
  several different input data values and observing
  the results
• Maintenance
• It is highly unlikely that this particular
  program will be of general use to anyone. Most
  likely, we'll want to update it with new
  functionality

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Next Week

• We've covered the general software development
  method
• It's time to start learning the C language!
• Have a great weekend!