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A High-Level Model For Software Development

A High-Level Model For Software Development. What is involved in the process of designing, writing and maintaining computer programs? What are some ways that an algorithm can be specified?. What Is Computer Science?. Review: Solving problems with the computer.

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A High-Level Model For Software Development

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  1. A High-Level Model For Software Development What is involved in the process of designing, writing and maintaining computer programs? What are some ways that an algorithm can be specified?

  2. What Is Computer Science? • Review: Solving problems with the computer

  3. A Model For Creating Computer Software • Specify the problem • Determine how to solve the problem • Implement the solution • Maintenance of the solution

  4. Specifying The Problem • Determine what problem will be solved by the computer • Verify the problem

  5. Determine How To Solve The Problem Specify the algorithm • Can be done in many ways • e.g., flowcharts, spreadsheets (more to come later in this section of notes) • Implementation independent! Check the algorithm

  6. Implement The Design Translating the high level algorithm to an actual programming language (e.g., Pascal) Test the program This step is covered in the balance of this course (and the next course, CPSC 233)

  7. Maintaining The Design Modify the program according to changing needs and to address problems (software bugs) Includes the application of techniques for good design (Software Engineering). Some in CPSC 233 (more in CPSC 333)

  8. What You Now Know: A Model For Creating Computer Software • Specify the problem • Determine how to solve the problem (algorithm) • Implement the solution • Maintenance of the solution

  9. What Is An Algorithm? • The steps needed to solve a problem • Characteristics • Specific • Unambiguous • Language independent

  10. Ways Of Specifying The Algorithm • Pseudo-code • Flowcharts

  11. Pseudo-Code • Employs 'programming-like' statements to depict the algorithm • No standard format (language independent)

  12. Pseudo-Code Statements • Display • Enter • Action • Decision making • Repetition • Statements are carried out in order • Example: Calling up a friend • Look up telephone number • Punch in telephone number • Wait for someone to answer • : :

  13. Variables • Are used with pseudo-code statements • Symbols (typically an alphabetic string e.g,, x, num, num1) used to store values • The value stored can change during the algorithm

  14. Constants • Are used with pseudo-code statements • They are values that cannot be changed

  15. Display • Used to show information • General format: • Line of text: Display 'Message' • Variable: Display Name of variable • Mixed display: Separate each item to be displayed with a comma • Example • Display 'Available credit limit $', limit

  16. Enter • Used to get information • Information is stored in a variable • General format: • Enter: Name of variable • Example: • Enter userName

  17. Pseudo-Code: Action • For computer programs it's usually an assignment statement (sets a variable to some value) • General form: • Variable = arithmetic expression • Example: • x = 2 • x = x + 1 • a = b * c

  18. Pseudo-Code: Decision Making • If-then • General form: • if (condition is met) then • statement(s) • Example: • if temperature < 0 then • wear a jacket • If-then-else • General form: • if (condition is met) then • statement(s) • else • statements(s)

  19. Pseudo-Code: Decision Making (2) • Example: • if (at work) then • Dress formally • else • Dress casually

  20. Pseudo-Code: Decision Making (3) • Types of conditions Symbol • Greater than > • Greater than or equal to ≥ • Less than < • Less than or equal to ≤ • Equal to = • Not equal to ≠

  21. Pseudo-Code: Repetition • repeat-until • while-do

  22. Pseudo-Code: Repetition (2) • repeat-until • Repeat at least once (check if condition is met after statement(s)) • General form: • repeat • statement(s) • until (condition is met) • Example: • repeat • Go up to buffet table • until full

  23. Pseudo-Code: Repetition (3) • while-do • Repeat zero or more times (check if condition is met before statement(s)) • General form: • while (condition is met) do • statement(s) • Example: • while students ask questions do • Answer questions

  24. Pseudo-Code: Fast Food Example • Use pseudo-code to specify the algorithm for a person who ordering food at a fast food restaurant. At the food counter, the person can either order or not order the following items: a burger, fries and a drink. After placing her order the person then goes to the cashier.

  25. Pseudo-Code: Fast Food Example • Approach counter • If want burger then • Order burger • If want fries then • Order fries • If want drink then • Order drink • Pay cashier

  26. Pseudo-Code: Grade Tabulator Example • Use pseudo-code to specify the algorithm for a grade tabulation program. The program will ask the instructor to enter in a percentage value for each student. Based on this value the program will determine if the student passed the course or not: • If the percentage is 50% or greater then the student passed the course and the message 'Student receives course credit' will appear. • Otherwise, if the percentage is below 50%, then the student failed the course and the message 'Student will not receive course credit' will appear. • As the instructor is entering grades, the program will automatically track the number of students who passed the course and the number of students that did not. The instructor indicates to the program that she has finished entering the grades by entering negative percentage (e.g., -1%) at which time the program displays the total number of students that passed and total that did not pass and it then ends execution.

  27. Pseudo-Code: Grade Tabulator Example • pass = 0 • fail = 0 • Display 'Enter percentage for student (negative percentage to end): ' • Enter percentage • While Percentage ≥0 do • If (percentage ≥ 50) then • Display 'Student receives course credit' • pass = pass + 1 • Else • Display 'Student will not receive course credit' • fail = fail + 1 • Display 'Enter percentage for student (negative percentage to end): ' • Enter percentage • Display 'Number of students that passed: ', pass • Display 'Number of students that failed: ', fail

  28. Summary Of Pseudo-Code Statements • Statement Purpose • Display Display information • Enter Get information • Action Perform an activity (not covered by the other statements) • Decision Choose between different alternatives • Repetition Perform a step multiple times • Variables are used in conjunction with these statements to store information. • Constants may be used to represent a value that does not ever change.

  29. Basic Flowchart Elements Action Terminator Input Output Off page Connector Decision c Arrow Variables and constants

  30. Flowchart: Fast Food Example • Draw a flowchart to outline the algorithm for a person who ordering food at a fast food restaurant. At the food counter, the person can either order or not order the following items: a burger, fries and a drink. After placing her order the person then goes to the cashier.

  31. Flowchart: Fast Food Example Approach counter Want burger? Order burger Y N Want fries? Order fries Y N Want Drink? Order drink Y N Pay cashier

  32. Flowchart: Grade Tabulator Example • Use a flowchart to specify the algorithm for a grade tabulation program. The program will ask the instructor to enter in a percentage value for each student. Based on this value the program will determine if the student passed the course or not: • If the percentage is 50% or greater then the student passed the course and the message 'Student receives course credit' will appear. • Otherwise, if the percentage is below 50%, then the student failed the course and the message 'Student will not receive course credit' will appear. • As the instructor is entering grades, the program will automatically track the number of students who passed the course and the number of students that did not. The instructor indicates to the program that she has finished entering the grades by entering negative percentage (e.g., -1%) at which time the program displays the total number of students that passed and total that did not pass and it then ends execution.

  33. Flowchart: Grade Tabulator Example Begin pass = 0 fail = 0 'Enter percentage for student (negative to end'): ' Percentage 1

  34. Flowchart: Grade Tabulator Example (2) 1 6 Percentage ≥0? N 2 Y Percentage ≥ 50? N 3 Y 4

  35. Flowchart: Grade Tabulator Example (3) 3 'Student will not receive course credit' fail = fail + 1 5

  36. Flowchart: Grade Tabulator Example (4) 4 'Student receives course credit' pass = pass + 1 5

  37. Flowchart: Grade Tabulator Example (5) 5 'Enter percentage for student (negative to end'): ' Percentage 6

  38. Flowchart: Grade Tabulator Example (6) 2 'Number of students that failed: ', fail 'Number of students that passed: ', pass End

  39. Summary • What are the major steps involved in creating software • Specification • Design • Implementation • Maintenance • How to layout out an algorithm using flowcharts and pseudo-code • What are the basic elements of algorithms • Input • Output • Decision-Making • Repetition • Action • Variables and constants

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