Structured Engineering Problem Solving and Logic Diagrams

1. Structured Engineering Problem Solving and Logic Diagrams Lecture 3 Winter Quarter

2. TOOLS FOR PROGRAM DEVELOPMENT • A variety of tools and techniques can be used in the process of program development • Useful for organizing the tasks in problem solving • Many of the tools are focused on the: • development or formulation of algorithms • representation of algorithms • refinement or structuring of algorithms Winter Quarter

3. TOOLS FOR PROGRAM DEVELOPMENT • Top-down design technique • Start with overall function and perform several step-wise refinements • Pseudo code • Artificial and informal language that helps programmers develop algorithms • Logic diagrams • Alternate representations of algorithms including graphic and state representations Winter Quarter

4. TOP-DOWN STEPWISE REFINEMENT • Begin with a single statement that conveys the overall function of the program. This is a complete (but simple) representation of the program. • Divide this "top" statement into a series of smaller tasks and list them in the order in which they must be performed to produce a first refinement. Winter Quarter

5. TOP-DOWN STEPWISE REFINEMENT • Next, refine each of the smaller tasks into yet smaller steps, defining specific "variables" as may be needed in this second refinement. • Continue refinement until algorithm is fully developed. • When combined with pseudo code, writing the program is normally straightforward. Winter Quarter

6. Top-Down Example • The Problem: The students in a class have taken their first quiz. The grades (in the range of 0 to 100) are available. Determine the class average on the quiz. • Givens: Grades, Possible range of legitimate grades. Winter Quarter

7. Top-Down Example (continued) • Unknowns: How many grades to be averaged? • Assumptions: A "grade" not in the range of expected grades could be used to indicate the that all of the legitimate grades have been entered. (Called "sentinel" or "flag".) Winter Quarter

8. Top-Down Example (continued) • Using pseudo code, we begin by representing the top: • Determine the class average for the quiz Winter Quarter

9. Top-Down Example (continued) • Next, perform the first refinement: • Determine the class average for the quiz • Initialize variables • Input, sum, and count quiz grades • Calculate and print the class average Winter Quarter

10. Top-Down Example (continued) • Next, refine each one of these smaller tasks: • Initialize variables • Initialize a running total to zero • Initialize a grade counter to zero Winter Quarter

11. Top-Down Example (continued) Input, sum, and count quiz grades Input the first grade While the user has not entered the "flag" Add this grade into the running total Add one to the grade counter Input next grade (possibly the "flag") Winter Quarter

12. Top-Down Example (continued) Calculate and print the class average If the grade counter is not zero Set the class average to the running total divided by the grade counter Print the average Else Print "No grades were entered" Winter Quarter

13. Handling Special Cases • Notice that the top-down refinement example included the handling of a "special case". • Many of you are aware of the special treatment that Windows gives to the extreme "special cases" (sometimes called the BSOD or Blue Screen of Death…) Winter Quarter

14. Handling Special Cases Winter Quarter

15. Some Types of Logic Diagrams • Flow Charts -- graphic representation of an algorithm • an aid to writing the program • no formal standards, but common guidelines • Action Diagrams -- technique for diagramming of control structures of a program • an outline of the computer application • what things happen, when, where, how many times Winter Quarter

16. Characteristics of Flow Charts • Useful tool in program development • Not a complete description of program • Not only tool to use • Made before writing the program • Program might differ from flowchart • Only executable statements are shown • Specific equations and tests not included • Every main and sub-program is charted Winter Quarter

17. Flow Charting Symbols • The commonly used flowcharting symbols follow • Refer to Section 9 of the H192 "Class Notes" for a more complete description of the various flowcharting symbols normally used Winter Quarter

18. Flow Charting Symbols Begin or End a Procedure: "Main Program" "Subprogram" Begin End Winter Quarter

19. Flow Charting Symbols Write to Screen: Read from Keyboard: Winter Quarter

20. Flow Charting Symbols Read from a File: Read from a File with a Check for End-of-File: Winter Quarter

21. Flow Charting Symbols Decision or Selection Structure: General Processing: Winter Quarter

22. Flow Charting Symbols Definite Loop: Indefinite Loop: Winter Quarter

23. Flow Charting Symbols On-Page Connectors: Off-Page Connectors: Winter Quarter

24. Flow Charting Symbols Call (or Invoke) a Subprogram: Winter Quarter

25. Daily Assignment F2 • Problem: There are a number of apples in a large box which must be sorted into baskets. An apple is either a "large red" one, a "small red" one, or a "green" one. • Develop a flow chart or algorithm to solve the problem Winter Quarter

26. Daily Assignment F2 Assumptions: 1. There are 3 empty baskets present and they are labeled: #1 – large red, #2 – small red, #3 – green 2. There are counters of some sort present. 3. The person sorting is not color blind and can tell the difference between large and small apples. 4. Only these three kinds of apples are in the large box. Winter Quarter

27. Daily Assignment F2 • Are there any unknowns? • Start with the overall problem • Develop the steps to solve the problem Winter Quarter