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Debugging an Operation

This session discusses the debugging process of an operation that failed to produce expected results. Students are guided through creating a testing harness and faced with unexpected outputs, leading them to question the correctness of their implementations. Utilizing string theory for mathematically modeling queues, the talk explores methodologies for identifying errors and improving problem-solving skills in programming. Attendees will walk away with practical strategies for debugging and understanding formal proofs of correctness.

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Debugging an Operation

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  1. Using a Failed Proof of Correctness as a Guide Debugging an Operation Joan Krone – Denison University Joseph Hollingsworth – Indiana University Southeast SIGCSE 2013 Special Session

  2. What Went Wrong? • Student implements an operation • Student creates a testing harness a small client program • Student runs the testing harness • Receives unexpected output • The operation doesn’t seem to do anything! SIGCSE 2013 Special Session

  3. Invert The outgoing Q equals the reverse of the incoming Q • #Q – incoming • Q – outgoing P_Queue is a preemptable queue • Has one additional operation – Inject SIGCSE 2013 Special Session

  4. String Theory Used for mathematically modeling a Queue •  - is the alphabet, e.g.,  = Z SIGCSE 2013 Special Session

  5. String Theory Used for mathematically modeling a Queue •  - is the alphabet, e.g.,  = Z • Example strings: • α = <4,22,3,17> string of 4 integers • β = < > empty string SIGCSE 2013 Special Session

  6. String Theory Used for mathematically modeling a Queue •  - is the alphabet, e.g.,  = Z • Example strings: • α = <4,22,3,17> string of 4 integers • β = < > empty string • Concatenation, Length, Reverse • <-5> o α o <101> = <-5,4,22,3,17,101> • |α| = 4 • Reverse(α) = <17,3,22,4> • Reverse(αo <101>) = <101,17,3,22,4> SIGCSE 2013 Special Session

  7. Testing Harness for Invert Output: q before Invert = <3,2,1> q after Invert = <3,2,1> SIGCSE 2013 Special Session

  8. How to Debug?I Could Try … • Using one of those genetic algorithms to make random mutations to my code … SIGCSE 2013 Special Session

  9. Or Maybe I Should … • Do that proof of correctness thingy that my professor showed us. SIGCSE 2013 Special Session

  10. Accessing theRESOLVE Web Interface SIGCSE 2013 Special Session

  11. Accessing Components SIGCSE 2013 Special Session

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