Program Design Methodology

Program Design Methodology

Why Plan?

Group projects without a plan will not work.
If you have not figured out the design before you begin coding, you may paint yourself into a corner and have to start over.
You will save time by planning.
You can verify that the algorithm works before coding.
The plan is your "blueprint" for software construction.

How do I Design an Algorithm?

Good question. There is no real answer to this question that works in all cases.
Algorithm design is the creative part of programming--a very human endeavor.
Computer programming is an art.
Elegant solutions are the simplest, but not all problems can be solved elegantly
Experience helps--patterns of problems and solutions emerge over time.

Some Help

Make sure that specifications are complete and make sense. Do you understand the problem?
Determine what the program is supposed to output.
What errors might occur while the program is running?
How should the program end?
Get answers to questions about the specifications before writing any code.

More Help

Break the problem into subproblems
For each subproblem
- write a concise problem statement to be sure you understand
- find an existing algorithm (if there is one), or create a new one
- design the data structures needed
- write out the steps (algorithm) for solving the subproblem
Create the code to implement your solution
- code and debug each function separately
- this is called procedural abstraction
- test all functions together

Diagramming Techniques

Structure Charts

Useful for decomposing the problem into smaller parts
Think of the boxes as functions in your program.
Relationship between the boxes--one function can call zero or more functions; a function can be called by zero or more functions.
Create the diagram from the top down.
The ultimate goal is functionally cohesive modules.
Modules have one task with all of the parts of the module contributing to the task.
Prevents side-effects
Minimizes coupling (loosely coupled vs. tightly coupled)

Implementation

Using the plan you developed, begin writing code.
Document as you code. (Function header comments)
Place detailed comments at the beginning of the program explaining the purpose of the program
Make comments for each function and use comments for unusual logic (driver1.cpp PrintList)

Testing

Testing can use about half the time for development of a system.
Test modules independently.
- drivers to test modules
- stubs to test modules for which functions have not been developed
- test cases that exercise all logical possibilities. Test normal and borderline cases.

Robustness

System Testing

Testing modules alone is not enough.
The whole system with all modules included needs to be tested.
Testing by end-users should be done since they are the ones who must ultimately accept the system. (Beta testers)
Systems that do not get the acceptance of the end users will fail even if well written. Software designed with the user in mind.

Debugging