CSC161 2010F, Class 33: Pointers and Arrays

Overview:
* Fun with Prospies.
* Questions on Exam 2.
* Pointers and Arrays.
* Your Questions.
* Labs.

Admin:
* We may have propsies today.  Yay!
* Question from a prospective 161 student: What is the workload like in
  this class compared to 151?
* EC for MD's Monday presentation.
* EC for Saturday's Men's Soccer game.
* EC for LoC truck.
* Reading for Monday: K&R 5.3 and Appendix B.  Send questions!
* Are there questions on Exam 2.  Bring them on Monday!

Fun with Prospies

* What is your name?
* Why are you visiting this class?
* [One question determined by the members of the class.]
* What would you like to know from this class?

Questions on Exam 2

* Do we have to use the debugger?
  * No.  Printfs, careful analysis, and more are also useful ways
    of identifying why your code fails.

Pointers and Arrays

* There's not a lot of difference between pointers and arrays.
        int y;
        int x;
        int z;
        int a[10];
        int *ip = &x;
  * You can often treat a pointer as an array
    printf ("%d", ip[0]);
    ip[0] = 5;
  * You can often treat an array as a pointer
    *a = 1;
  * a[i] = X is the same as *(a+i) = X;

* Ways to distinguish arrays and pointers
  * You can declare the size of the chunk of memory an array requires.
  * You can change what a pointer points to

Your Questions on the Arrays/Pointers Reading

* What does *(a+1) mean?
  * The C compiler knows the type of thing that a points to.  So when
    you increment by 1, it says "that's 1 THING, not 1 byte"

* Can a pointer point to a pointer? If so, can you access the value by 
  using multiple * commands?
  * Yes.  A pointer to a pointer even has a traditional name: a Handle
  * Info in 5.9 or so.

* In page 105 about the comparison between the pointers and arrays, what 
  is the difference in the declaration of arrays and pointers? 
* Please explain (*t = *s) != '\0'. 
  
* I don't understand what the point of allocp and afree are.  Can 
  you just talk about them a little?  
* Could you provide some examples in class illustrating the situations 
  where it would be prudent to use pointers in a program?

Labs