Debugging (1)

Admin
* Welcome back from break!
* Sorry about the pre-break breaks
* I should be available the rest of the semester, and maybe even a
  bit organized.
* Debugging, testing/experimentation, and design for the next few weeks

Debugging
* Why? - Most code is buggy (which we learn from our unit tests)
* What?
  - "Where" is the bug?
  - What caused the bug?
* How?
  - Look at error messages for crash "Segmentation Fault"
  - Print statements to track program state
    * In C, print statements can eliminate segfaults.
      E.g.,
        int foo[10];
        printf ("I declared foo.\n");
        foo[10] = 4;
    * Someone talented with a debugger can acheive same result with
      much less effort.
  - Use a debugger
  - Static analysis - Go through the program by hand
    - Extreme: Write pre/post, invariants, etc.
  - Program analyzer 
    - Static - -Wall
    - Dynamic - E.g. valgrind for checking memory

Example Code 
* int ibs(int A[], int len, int v) - returns index or -1
* Explore 
  * Try different sizes of the array
  * Try the empty array
  * Try odd and even length arrays
  * Write unit tests (yay!)
  * Write an interactive experiment
    Idea: ibs-expt VAL A[0] A[1] ... A[N-1]
* Fix

gdb basics

If time: Designing a list interface (because we often do things
too specifically)