1. CSC 110 – Fluency in Information Technology Chapter 7: An Introduction to Debugging
Dr. Curry Guinn

2. Today’s Class Debugging Laboratory Activities
Warning: Some material in this lecture is not in the book!
Laboratory Activities

3. Debugging Debugging == troubleshooting
What kinds of errors do we humans make when working with computers?
Syntax errors
We violate lexical structure
Case sensitivity is a common gotcha
Wrong data
Wrong command

4. Harvard Mark II

5. Errors that aren’t the user’s fault
Hardware errors (The First Bug)
Burnt chips
Software errors
Careless programming
Logical design errors

6. How Systems Ought To Be Developed
Software life-cycle
Over 50 years of creating software has taught us a few things
Can apply to any project, manufacturing, creation of a product or service

7. The Software Life-Cycle
Lessons learned over the past 5 decades of programming
Software engineering is the application of a systematic and disciplined approach to the development, testing, and maintenance of a program.
5 stages:
Analysis
Design
Coding
Testing
Operation

8. 1. Analysis What do the clients want?
What will the users of the product experience?
Feasibility study
Is it possible given
Time
Money
Knowledge
Requirements specification
Specific breakdown of features

9. 2. Design
Take requirements specification and turn it into a program/product design
What materials do you need?
What processes will be necessary to produce the product?
Design the system abstractly
Architecture: Blueprints
Car design: Computer-aided design drawings

10. 3. Coding/Creating/Constructing
Implementation
Writing the code or
Erecting the building
If the design is good, this is really easy.

11. 4. Testing Verifying the code meets the specs Unit testing
Does the product satisfy the requirements document?
Unit testing
Test components of product individually
Integration testing
Combine working components and make sure they function together
Case in point: Mars orbiter

12. 5. Operation (Maintenance)
Software maintenance
Shown to be The most time-consuming
Expensive
70% of cost

13. The Major Steps during Debugging
Reproducing the error
Must be able to determine the sequence of steps that lead to the error
Determine exactly what the faulty behavior is
Eliminate the “obvious” causes
Divide the process to determine within which part the error is occurring
When you reach a dead end, reassess the assumptions you made along the way
As you work, make predictions about what should happen and verify that your predictions are fulfilled

14. An Example
The intended web page:

15. What does it look like now?
Butterflies
Look at the source
Butterfly.zip

16. Debugging Steps Reproduce the Error Reload the page… still there
If we had another browser (like Netscape or Mozilla) we might try that browser and see if it looks the same
If it does, we know it’s something in the .htm code

17. What exactly is wrong At least 2 obvious problems Should be four rows
Where are the pictures?

18. Identifying Obvious Problems
Maybe a tag is misspelled
Maybe a <tag> is missing its </tag>
Maybe a tag is just missing
For the images,
Check relative link structure

19. Divide and Conquer The problem must be in the <img> tag
Let’s open up something that color codes
Getting the quotations right
Correcting misspellings
Table headings

20. … And now for the Lab
Activity 1: Download and unzip the following webpage/image combo:
Load the web page labexample1.htm in your browser. It should look like the next slide.

22. Activity 1: Debugging an HTML page
Try and track down the various problems in the html source

23. Activity 2: Testing that Behaviors Match Specifications
Download the following tic tac toe game:
Also download the following .doc file

24. Activity 2 continued
The specs.doc file list the behaviors expected by the tic tac toe program.
Conduct tests to determine whether the program acts accordingly
If so, mark that condition as Pass within specs.doc.
If not, mark that condition as Fail, indicate how the behavior fails, and describe the sequence of steps needed to reproduce the behavior.

25. Wrap-up
Homework
Read Chapter 8
Ch 9 only homework due 09/18