Chapter 3: Modularization

1. Chapter 3:Modularization

2. Objectives • Understanding Documentation • Learn about documentation • Learn about the advantages of modularization • Learn how to modularize a program • Declare local and global variables and constants • Create hierarchy charts

3. Documentation • Documentation • All supporting material that goes with a program • Two major categories: for users and for programmers • User Documentation: End users (people who use computer programs) • Program Documentation • Internal program documentation: comments within code • External program documentation: supporting paperwork written before programming begins

4. Output Documentation Figure 3-2 Inventory records displayed in a GUI environment Figure 3-3 Inventory records displayed in a running program

5. Input Documentation • Describes what input is available to produce the output • File description: • Describes data stored in a file • Indicates fields, data types, and lengths Figure 3-6 Inventory file description

6. Completing Documentation • Program documentation may contain: • Output design • Input description • Flowcharts • Pseudocode • Program code listing • User documentation may contain: • Manuals • Instructional material • Operating instructions

7. Modularization • Modularization: breaking a large program into modules • Advantages of modularization: • Provides abstraction • Allows multiple programmers to work simultaneously • Allows code reuse • Makes identifying structures easier

8. Modularization • Module: • Unit of code that performs one small task • Called a subroutine, procedure, function, or method • Invoke (call) a method is to execute it • Callingmethod invokes the called method • Program contains unlimited number of methods • Each method can be called unlimited number of times

9. Modularization Provides Abstraction • Focuses on important properties while ignoring non-essential details • Avoids low-level details • Makes complex tasks look simple • High-level programming languages allow English-like vocabulary • One statement corresponds to dozens of machine instructions • Modules provide another way to achieve abstraction

10. To-do list with abstraction Do laundry Call Aunt Nan Start term paper To-do list without abstraction Pick up laundry basket Put laundry basket in car Drive to laundromat Get out of car with basket Walk into laundromat Set basket down . . . Modularization Provides Abstraction (continued)

11. Modularization Allows Multiple Programmers to Work on a Problem • Commercial programs rarely written by a single programmer • Development time is significantly reduced • Large programming projects can be divided into modules • Modules can be written by different programmers or programming teams

12. Modularization Allows You to Reuse Your Work • Subroutines that are useful should be used more than once in a program • Example: routine that checks the current date • Instructions placed in their own module are easy to port to other applications • Reusability:the ability to use modules in a variety of applications • Reliability: assurance that a module has been tested and proven to function correctly • Reliable software saves times and money

13. Modularizing a Program • Most programs contain a main program • Contains the mainline logic • Accesses other modules or subroutines • Rules for naming modules different for every programming language • For this text: • Must be one word • Should be meaningful • Followed by a set of parentheses • Corresponds to module naming in Java, C++, C#

14. Modularizing a Program (continued) Table 3-1 Suggested identifiers for a module that calculates an employee’s gross pay

15. Modularizing a Program (continued) • Calling program (or calling module): one that uses another module • Flowchart symbol for calling a module: rectangle with bar across the top • Flowchart for the module • Start symbol: contains module name • Stop symbol: contains exit or return • When a module is called, logic transfers to the model • When module ends, logic transfers back to the caller

16. Figure 3-8 Sample logic Figure 3-9 Logic from Figure 3-8 using a method

17. Figure 3-10 Logic from Figure 3-9 using two methods

18. Modularizing a Program (continued) • Method is encapsulated in another method if it is contained in another method • Knowing when to break a module into its own subroutines or submodules is an art • Best practice: place together statements that contribute to one specific task • Functional cohesion: extent to which the statements contribute to the same task