Programming Logic and Design Fourth Edition, Comprehensive

1. Programming Logic and Design Fourth Edition, Comprehensive Chapter 4 Designing and Writing a Complete Program

2. Programming Logic and Design, Introductory, Fourth Edition 2 Objectives Plan the mainline logic for a complete program Describe typical housekeeping tasks Describe tasks typically performed in the main loop of a program Describe tasks performed in the end-of-job module Understand the need for good program design

3. Programming Logic and Design, Introductory, Fourth Edition 3 Objectives (continued) Appreciate the advantages of storing program components in separate files Select superior variable and module names Design clear module statements Understand the need for maintaining good programming habits

4. Programming Logic and Design, Introductory, Fourth Edition 4 Understanding the Mainline Logical Flow Through a Program Understand what the goals are Ask the user to clarify if necessary

5. Programming Logic and Design, Introductory, Fourth Edition 5 Understanding the Mainline Logical Flow Through a Program (continued) Ensure you have all the data required to produce the desired output

6. Programming Logic and Design, Introductory, Fourth Edition 6 Understanding the Mainline Logical Flow Through a Program (continued)

7. Programming Logic and Design, Introductory, Fourth Edition 7 Understanding the Mainline Logical Flow Through a Program (continued) Procedural program: one procedure follows another from beginning to end Mainline logic has three distinct parts: Housekeeping: steps to get ready Main loop: instructions executed for every input record End-of-job: steps taken at end of program Break the logic down into at least three modules

8. Programming Logic and Design, Introductory, Fourth Edition 8 Understanding the Mainline Logical Flow Through a Program (continued)

9. Programming Logic and Design, Introductory, Fourth Edition 9 Understanding the Mainline Logical Flow Through a Program (continued) Modularization of the program: Keeps the job manageable Allows multiple programmers to work simultaneously Keeps the program structured

10. Programming Logic and Design, Introductory, Fourth Edition 10 Housekeeping Tasks Housekeeping tasks: include all steps that occur at the beginning of the program Declare variables Assumption in this book is the variables will be global variables! Open files Perform one-time-only tasks such as printing headings Read the first input record

11. Programming Logic and Design, Introductory, Fourth Edition 11 Declaring Variables Assign identifiers to memory locations Specify the name and data type Use meaningful names and follow standards Prefixes may be used to group related variables Declare a variable for each field in a data file

12. Programming Logic and Design, Introductory, Fourth Edition 12 Declaring Variables (continued)

13. Programming Logic and Design, Introductory, Fourth Edition 13 Declaring Variables (continued) Group name:  Name for a group of associated variables Can handle the entire group with a single instruction

14. Programming Logic and Design, Introductory, Fourth Edition 14 Declaring Variables (continued) Initializing (or defining) the variable: providing an initial value Some languages provide default initial values Other languages leave variables with an unknown or garbage value Variables representing data fields in files do not need to be initialized

15. Programming Logic and Design, Introductory, Fourth Edition 15 Declaring Variables (continued) Can use variables for report headings Embed any required spaces Heading can be printed using these variables

16. Programming Logic and Design, Introductory, Fourth Edition 16 Declaring Variables (continued) Every language provides methods for: [ NOT TRUE! ] Advancing the paper to top of page Printing single, double, or triple spaced lines Use annotation symbol to show variables

17. Programming Logic and Design, Introductory, Fourth Edition 17 Opening Files Specify file name and path (location) Issue a file open command If no input file is opened, input may be accepted from the standard input device (e.g., keyboard) You must open both input and output files to be used, including printer output device If no output file is opened, standard output device (e.g., monitor) may be used

18. Programming Logic and Design, Introductory, Fourth Edition 18 A One-Time-Only TaskPrinting Headings Printing headings for reports usually is done at beginning of the program

19. Programming Logic and Design, Introductory, Fourth Edition 19 Reading the First Input Record Reading the first input record is the last housekeeping task Interactive application:  Interacts with users via keyboard or mouse input Program pauses when the read command is executed until the user enters data Delimiter: a character designated as a separator between data values Prompt: an output statement that asks the user to enter specific data

20. Programming Logic and Design, Introductory, Fourth Edition 20 Reading the First Input Record (continued) Interactive input:

21. Programming Logic and Design, Introductory, Fourth Edition 21 Reading the First Input Record (continued) Input from a data file: Input from a data file using a group name:

22. Programming Logic and Design, Introductory, Fourth Edition 22 Checking for the End of File ( EOF ) First task after housekeeping For an interactive program, EOF may be determined when: User enters a predetermined sentinel value User selects a screen option using a mouse For input from a file, the input device recognizes EOF If no data in the file, EOF occurs on the first read If there is data, each record is processed before the next read occurs

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26. Programming Logic and Design, Introductory, Fourth Edition 26 Handling the report headings in a separate module:

27. Programming Logic and Design, Introductory, Fourth Edition 27 Writing the Main Loop Each data record passes through the main loop once Inventory program main loop steps: Calculate the profit for an item Print the item’s information on the report Read the next inventory record

28. Programming Logic and Design, Introductory, Fourth Edition 28 Writing the Main Loop (continued) Must declare additional variables for calculation results

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31. Programming Logic and Design, Introductory, Fourth Edition 31 Performing End-of-Job Tasks End-of-job tasks may include: Printing summaries or grand totals Printing “End of Report” message Closing any open files Footer line (or footer): end-of-job message line

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35. Programming Logic and Design, Introductory, Fourth Edition 35 Understanding the Need for Good Program Design Good design is: Critical for very large programs Needed to guarantee that components work together properly Well-designed program modules should work: As stand-alone modules  As part of larger systems

36. Programming Logic and Design, Introductory, Fourth Edition 36 Storing Program Components in Separate Files Large programs may contain hundreds of variables and thousands of lines of code Manage lengthy programs by breaking into modules Many languages allow program components to be stored in separate files Storing components separately simplifies reuse Accessing modules from separate files is done with a statement like include, import, or copy

37. Programming Logic and Design, Introductory, Fourth Edition 37 Storing Program Components in Separate Files (continued)

38. Programming Logic and Design, Introductory, Fourth Edition 38 Storing Program Components in Separate Files (continued) Advantages of storing components separately: Simplifies reuse Can be provided in compiled form only, to hide details Implementation hiding: hiding details of how a program or module works

39. Programming Logic and Design, Introductory, Fourth Edition 39 Selecting Variable and Module Names Using meaningful names: Improves code readability Is a form of self-documenting the program Use pronounceable names Commonly used abbreviations are ok (e.g., SSN) Avoid digits in a name to avoid confusing: Zeros and O’s Ones and lowercase L’s

40. Programming Logic and Design, Introductory, Fourth Edition 40 Designing Clear Module Statements Follow these rules: Select good identifier names Avoid confusing line breaks Use temporary variables to clarify long statements Use constants where appropriate

41. Programming Logic and Design, Introductory, Fourth Edition 41 Avoiding Confusing Line Breaks Free-form coding allows programmer to decide where to break lines of code

42. Programming Logic and Design, Introductory, Fourth Edition 42 Using Temporary Variables to Clarify Long Statements Use temporary variables to store intermediate results

43. Programming Logic and Design, Introductory, Fourth Edition 43 Using Constants Where Appropriate Named constant: a constant whose value never changes during execution Advantages Improves code readability If the value changes later, there is only one place in the code to make the change Usually written with all uppercase letters ATHLETIC_FEE TUITION_PER_CREDIT_HOUR

44. Programming Logic and Design, Introductory, Fourth Edition 44 Using Constants Where Appropriate (continued)

45. Programming Logic and Design, Introductory, Fourth Edition 45 Maintaining Good Programming Habits Program will be better written if you plan before you code Walk through program logic on paper before coding (desk-checking) Select good variable and module names for readability

46. Programming Logic and Design, Introductory, Fourth Edition 46 Summary Three steps to designing a good program: Understand the output that is required Ensure you have the necessary input data Plan the mainline logic Housekeeping tasks done at the beginning of the program: declaring variables, opening files, printing headings Main loop is controlled by EOF decision Each data record passes through the main loop once

47. Programming Logic and Design, Introductory, Fourth Edition 47 Summary (continued) End-of-job steps done at end of the program: printing summaries, closing files Good design becomes more critical as programs get larger Program components can be stored in separate files Select meaningful, pronounceable names Avoid confusing line breaks, use temporary variables, and use constants where appropriate