Errors

1
Errors

• Definitions
• What to do about them?

2
Agenda

• Announcements
• Exam 2 will be curved by 10 points
• Learn your TAs name!
• Reminder
• Lab attendance required
• Lecture
• Errors

3
Motivation for Topic

• Testing
• Process of finding errors
• Ultimate review of specifications, design
  coding
• Purpose
• Guarantee all elements of an application work
  together properly, function as expected, and meet
  performance criteria
• Why is it so difficult?
• Debugging
• Process of isolating and repairing errors

4
Introduction to Errors

• Definitions
• Error
• Mistake made by human
• Physical mistake made
• Types of Errors
• Type I - Errors of Omission
• Type II - Errors of Comission
• Validation
• Verification

• Fault
• An incorrect step, process, or data definition
  in a computer program. IEEE Standard
• Programming or design errors where the delivered
  program does not conform to the specification
• Manifestation of error
• Failure
• A departure from the systems intended
  operational behavior
• Detected during execution

5
Examples

• Errors
• Typo (/-)
• De-referencing a pointer instead of assigning
• Misspelling a variable
• Algorithm error O(nn) vs O(nlogn) sort

• Fault
• X AB vs X AB
• Value of X is manifestation of error
• Failure
• XBalance
• ACurrent Balance
• BDeposit/Withdrawal
• Result wrong balance
• Sort takes too long

6
How to...

• Try to find faults
• Testing
• You try to prevent errors
• Coding Standards
• Programming discipline
• Sometimes you can only test for failures

7
Issues associated with errors

• Try to prevent them in the first place
• You cant find all of them
• Find them and fix them early
• Incremental development
• You cant find all of them
• Know what you are looking for when you are
  testing
• You cant find all of them